SVGHMI: DropDown widget now using new class based style svghmi
authorEdouard Tisserant
Tue, 15 Dec 2020 13:43:21 +0100
branchsvghmi
changeset 3090 9e172e4e50c7
parent 3089 10b2e620b57f
child 3091 f475f39713aa
SVGHMI: DropDown widget now using new class based style
svghmi/gen_index_xhtml.xslt
svghmi/widget_dropdown.ysl2
--- a/svghmi/gen_index_xhtml.xslt	Thu Dec 10 15:48:15 2020 +0100
+++ b/svghmi/gen_index_xhtml.xslt	Tue Dec 15 13:43:21 2020 +0100
@@ -1901,8 +1901,6 @@
       </xsl:with-param>
       <xsl:with-param name="mandatory" select="'no'"/>
     </xsl:call-template>
-    <xsl:text>
-</xsl:text>
   </xsl:template>
   <xsl:template mode="widget_class" match="widget[@type='CircularBar']">
     <xsl:text>class CircularBarWidget extends Widget{
@@ -3063,6 +3061,496 @@
     <xsl:text>
 </xsl:text>
   </xsl:template>
+  <xsl:template mode="widget_class" match="widget[@type='DropDown']">
+    <xsl:text>    class DropDownWidget extends Widget{
+</xsl:text>
+    <xsl:text>        dispatch(value) {
+</xsl:text>
+    <xsl:text>            if(!this.opened) this.set_selection(value);
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        init() {
+</xsl:text>
+    <xsl:text>            this.button_elt.onclick = this.on_button_click.bind(this);
+</xsl:text>
+    <xsl:text>            // Save original size of rectangle
+</xsl:text>
+    <xsl:text>            this.box_bbox = this.box_elt.getBBox()
+</xsl:text>
+    <xsl:text>
+</xsl:text>
+    <xsl:text>            // Compute margins
+</xsl:text>
+    <xsl:text>            let text_bbox = this.text_elt.getBBox();
+</xsl:text>
+    <xsl:text>            let lmargin = text_bbox.x - this.box_bbox.x;
+</xsl:text>
+    <xsl:text>            let tmargin = text_bbox.y - this.box_bbox.y;
+</xsl:text>
+    <xsl:text>            this.margins = [lmargin, tmargin].map(x =&gt; Math.max(x,0));
+</xsl:text>
+    <xsl:text>
+</xsl:text>
+    <xsl:text>            // Index of first visible element in the menu, when opened
+</xsl:text>
+    <xsl:text>            this.menu_offset = 0;
+</xsl:text>
+    <xsl:text>
+</xsl:text>
+    <xsl:text>            // How mutch to lift the menu vertically so that it does not cross bottom border
+</xsl:text>
+    <xsl:text>            this.lift = 0;
+</xsl:text>
+    <xsl:text>
+</xsl:text>
+    <xsl:text>            // Event handlers cannot be object method ('this' is unknown)
+</xsl:text>
+    <xsl:text>            // as a workaround, handler given to addEventListener is bound in advance.
+</xsl:text>
+    <xsl:text>            this.bound_close_on_click_elsewhere = this.close_on_click_elsewhere.bind(this);
+</xsl:text>
+    <xsl:text>            this.bound_on_selection_click = this.on_selection_click.bind(this);
+</xsl:text>
+    <xsl:text>            this.bound_on_backward_click = this.on_backward_click.bind(this);
+</xsl:text>
+    <xsl:text>            this.bound_on_forward_click = this.on_forward_click.bind(this);
+</xsl:text>
+    <xsl:text>            this.opened = false;
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        on_button_click() {
+</xsl:text>
+    <xsl:text>            this.open();
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        // Called when a menu entry is clicked
+</xsl:text>
+    <xsl:text>        on_selection_click(selection) {
+</xsl:text>
+    <xsl:text>            this.close();
+</xsl:text>
+    <xsl:text>            this.apply_hmi_value(0, selection);
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        on_backward_click(){
+</xsl:text>
+    <xsl:text>            this.scroll(false);
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        on_forward_click(){
+</xsl:text>
+    <xsl:text>            this.scroll(true);
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        set_selection(value) {
+</xsl:text>
+    <xsl:text>            let display_str;
+</xsl:text>
+    <xsl:text>            if(value &gt;= 0 &amp;&amp; value &lt; this.content.length){
+</xsl:text>
+    <xsl:text>                // if valid selection resolve content
+</xsl:text>
+    <xsl:text>                display_str = this.content[value];
+</xsl:text>
+    <xsl:text>                this.last_selection = value;
+</xsl:text>
+    <xsl:text>            } else {
+</xsl:text>
+    <xsl:text>                // otherwise show problem
+</xsl:text>
+    <xsl:text>                display_str = "?"+String(value)+"?";
+</xsl:text>
+    <xsl:text>            }
+</xsl:text>
+    <xsl:text>            // It is assumed that first span always stays,
+</xsl:text>
+    <xsl:text>            // and contains selection when menu is closed
+</xsl:text>
+    <xsl:text>            this.text_elt.firstElementChild.textContent = display_str;
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        grow_text(up_to) {
+</xsl:text>
+    <xsl:text>            let count = 1;
+</xsl:text>
+    <xsl:text>            let txt = this.text_elt; 
+</xsl:text>
+    <xsl:text>            let first = txt.firstElementChild;
+</xsl:text>
+    <xsl:text>            // Real world (pixels) boundaries of current page
+</xsl:text>
+    <xsl:text>            let bounds = svg_root.getBoundingClientRect(); 
+</xsl:text>
+    <xsl:text>            this.lift = 0;
+</xsl:text>
+    <xsl:text>            while(count &lt; up_to) {
+</xsl:text>
+    <xsl:text>                let next = first.cloneNode();
+</xsl:text>
+    <xsl:text>                // relative line by line text flow instead of absolute y coordinate
+</xsl:text>
+    <xsl:text>                next.removeAttribute("y");
+</xsl:text>
+    <xsl:text>                next.setAttribute("dy", "1.1em");
+</xsl:text>
+    <xsl:text>                // default content to allow computing text element bbox
+</xsl:text>
+    <xsl:text>                next.textContent = "...";
+</xsl:text>
+    <xsl:text>                // append new span to text element
+</xsl:text>
+    <xsl:text>                txt.appendChild(next);
+</xsl:text>
+    <xsl:text>                // now check if text extended by one row fits to page
+</xsl:text>
+    <xsl:text>                // FIXME : exclude margins to be more accurate on box size
+</xsl:text>
+    <xsl:text>                let rect = txt.getBoundingClientRect();
+</xsl:text>
+    <xsl:text>                if(rect.bottom &gt; bounds.bottom){
+</xsl:text>
+    <xsl:text>                    // in case of overflow at the bottom, lift up one row
+</xsl:text>
+    <xsl:text>                    let backup = first.getAttribute("dy");
+</xsl:text>
+    <xsl:text>                    // apply lift asr a dy added too first span (y attrib stays)
+</xsl:text>
+    <xsl:text>                    first.setAttribute("dy", "-"+String((this.lift+1)*1.1)+"em");
+</xsl:text>
+    <xsl:text>                    rect = txt.getBoundingClientRect();
+</xsl:text>
+    <xsl:text>                    if(rect.top &gt; bounds.top){
+</xsl:text>
+    <xsl:text>                        this.lift += 1;
+</xsl:text>
+    <xsl:text>                    } else {
+</xsl:text>
+    <xsl:text>                        // if it goes over the top, then backtrack
+</xsl:text>
+    <xsl:text>                        // restore dy attribute on first span
+</xsl:text>
+    <xsl:text>                        if(backup)
+</xsl:text>
+    <xsl:text>                            first.setAttribute("dy", backup);
+</xsl:text>
+    <xsl:text>                        else
+</xsl:text>
+    <xsl:text>                            first.removeAttribute("dy");
+</xsl:text>
+    <xsl:text>                        // remove unwanted child
+</xsl:text>
+    <xsl:text>                        txt.removeChild(next);
+</xsl:text>
+    <xsl:text>                        return count;
+</xsl:text>
+    <xsl:text>                    }
+</xsl:text>
+    <xsl:text>                }
+</xsl:text>
+    <xsl:text>                count++;
+</xsl:text>
+    <xsl:text>            }
+</xsl:text>
+    <xsl:text>            return count;
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        close_on_click_elsewhere(e) {
+</xsl:text>
+    <xsl:text>            // inhibit events not targetting spans (menu items)
+</xsl:text>
+    <xsl:text>            if(e.target.parentNode !== this.text_elt){
+</xsl:text>
+    <xsl:text>                e.stopPropagation();
+</xsl:text>
+    <xsl:text>                // close menu in case click is outside box
+</xsl:text>
+    <xsl:text>                if(e.target !== this.box_elt)
+</xsl:text>
+    <xsl:text>                    this.close();
+</xsl:text>
+    <xsl:text>            }
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        close(){
+</xsl:text>
+    <xsl:text>            // Stop hogging all click events
+</xsl:text>
+    <xsl:text>            svg_root.removeEventListener("click", this.bound_close_on_click_elsewhere, true);
+</xsl:text>
+    <xsl:text>            // Restore position and sixe of widget elements
+</xsl:text>
+    <xsl:text>            this.reset_text();
+</xsl:text>
+    <xsl:text>            this.reset_box();
+</xsl:text>
+    <xsl:text>            // Put the button back in place
+</xsl:text>
+    <xsl:text>            this.element.appendChild(this.button_elt);
+</xsl:text>
+    <xsl:text>            // Mark as closed (to allow dispatch)
+</xsl:text>
+    <xsl:text>            this.opened = false;
+</xsl:text>
+    <xsl:text>            // Dispatch last cached value
+</xsl:text>
+    <xsl:text>            this.apply_cache();
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        // Set text content when content is smaller than menu (no scrolling)
+</xsl:text>
+    <xsl:text>        set_complete_text(){
+</xsl:text>
+    <xsl:text>            let spans = this.text_elt.children; 
+</xsl:text>
+    <xsl:text>            let c = 0;
+</xsl:text>
+    <xsl:text>            for(let item of this.content){
+</xsl:text>
+    <xsl:text>                let span=spans[c];
+</xsl:text>
+    <xsl:text>                span.textContent = item;
+</xsl:text>
+    <xsl:text>                span.onclick = (evt) =&gt; this.bound_on_selection_click(c);
+</xsl:text>
+    <xsl:text>                c++;
+</xsl:text>
+    <xsl:text>            }
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        // Move partial view :
+</xsl:text>
+    <xsl:text>        // false : upward, lower value
+</xsl:text>
+    <xsl:text>        // true  : downward, higher value
+</xsl:text>
+    <xsl:text>        scroll(forward){
+</xsl:text>
+    <xsl:text>            let contentlength = this.content.length;
+</xsl:text>
+    <xsl:text>            let spans = this.text_elt.children; 
+</xsl:text>
+    <xsl:text>            let spanslength = spans.length;
+</xsl:text>
+    <xsl:text>            // reduce accounted menu size according to jumps
+</xsl:text>
+    <xsl:text>            if(this.menu_offset != 0) spanslength--;
+</xsl:text>
+    <xsl:text>            if(this.menu_offset &lt; contentlength - 1) spanslength--;
+</xsl:text>
+    <xsl:text>            if(forward){
+</xsl:text>
+    <xsl:text>                this.menu_offset = Math.min(
+</xsl:text>
+    <xsl:text>                    contentlength - spans.length + 1, 
+</xsl:text>
+    <xsl:text>                    this.menu_offset + spanslength);
+</xsl:text>
+    <xsl:text>            }else{
+</xsl:text>
+    <xsl:text>                this.menu_offset = Math.max(
+</xsl:text>
+    <xsl:text>                    0, 
+</xsl:text>
+    <xsl:text>                    this.menu_offset - spanslength);
+</xsl:text>
+    <xsl:text>            }
+</xsl:text>
+    <xsl:text>            this.set_partial_text();
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        // Setup partial view text content
+</xsl:text>
+    <xsl:text>        // with jumps at first and last entry when appropriate
+</xsl:text>
+    <xsl:text>        set_partial_text(){
+</xsl:text>
+    <xsl:text>            let spans = this.text_elt.children; 
+</xsl:text>
+    <xsl:text>            let contentlength = this.content.length;
+</xsl:text>
+    <xsl:text>            let spanslength = spans.length;
+</xsl:text>
+    <xsl:text>            let i = this.menu_offset, c = 0;
+</xsl:text>
+    <xsl:text>            while(c &lt; spanslength){
+</xsl:text>
+    <xsl:text>                let span=spans[c];
+</xsl:text>
+    <xsl:text>                // backward jump only present if not exactly at start
+</xsl:text>
+    <xsl:text>                if(c == 0 &amp;&amp; i != 0){
+</xsl:text>
+    <xsl:text>                    span.textContent = "&#x2191;  &#x2191;  &#x2191;";
+</xsl:text>
+    <xsl:text>                    span.onclick = this.bound_on_backward_click;
+</xsl:text>
+    <xsl:text>                // presence of forward jump when not right at the end
+</xsl:text>
+    <xsl:text>                }else if(c == spanslength-1 &amp;&amp; i &lt; contentlength - 1){
+</xsl:text>
+    <xsl:text>                    span.textContent = "&#x2193;  &#x2193;  &#x2193;";
+</xsl:text>
+    <xsl:text>                    span.onclick = this.bound_on_forward_click;
+</xsl:text>
+    <xsl:text>                // otherwise normal content
+</xsl:text>
+    <xsl:text>                }else{
+</xsl:text>
+    <xsl:text>                    span.textContent = this.content[i];
+</xsl:text>
+    <xsl:text>                    let sel = i;
+</xsl:text>
+    <xsl:text>                    span.onclick = (evt) =&gt; this.bound_on_selection_click(sel);
+</xsl:text>
+    <xsl:text>                    i++;
+</xsl:text>
+    <xsl:text>                }
+</xsl:text>
+    <xsl:text>                c++;
+</xsl:text>
+    <xsl:text>            }
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        open(){
+</xsl:text>
+    <xsl:text>            let length = this.content.length;
+</xsl:text>
+    <xsl:text>            // systematically reset text, to strip eventual whitespace spans
+</xsl:text>
+    <xsl:text>            this.reset_text();
+</xsl:text>
+    <xsl:text>            // grow as much as needed or possible
+</xsl:text>
+    <xsl:text>            let slots = this.grow_text(length);
+</xsl:text>
+    <xsl:text>            // Depending on final size
+</xsl:text>
+    <xsl:text>            if(slots == length) {
+</xsl:text>
+    <xsl:text>                // show all at once
+</xsl:text>
+    <xsl:text>                this.set_complete_text();
+</xsl:text>
+    <xsl:text>            } else {
+</xsl:text>
+    <xsl:text>                // eventualy align menu to current selection, compensating for lift
+</xsl:text>
+    <xsl:text>                let offset = this.last_selection - this.lift;
+</xsl:text>
+    <xsl:text>                if(offset &gt; 0)
+</xsl:text>
+    <xsl:text>                    this.menu_offset = Math.min(offset + 1, length - slots + 1);
+</xsl:text>
+    <xsl:text>                else
+</xsl:text>
+    <xsl:text>                    this.menu_offset = 0;
+</xsl:text>
+    <xsl:text>                // show surrounding values
+</xsl:text>
+    <xsl:text>                this.set_partial_text();
+</xsl:text>
+    <xsl:text>            }
+</xsl:text>
+    <xsl:text>            // Now that text size is known, we can set the box around it
+</xsl:text>
+    <xsl:text>            this.adjust_box_to_text();
+</xsl:text>
+    <xsl:text>            // Take button out until menu closed
+</xsl:text>
+    <xsl:text>            this.element.removeChild(this.button_elt);
+</xsl:text>
+    <xsl:text>            // Rise widget to top by moving it to last position among siblings
+</xsl:text>
+    <xsl:text>            this.element.parentNode.appendChild(this.element.parentNode.removeChild(this.element));
+</xsl:text>
+    <xsl:text>            // disable interaction with background
+</xsl:text>
+    <xsl:text>            svg_root.addEventListener("click", this.bound_close_on_click_elsewhere, true);
+</xsl:text>
+    <xsl:text>            // mark as open
+</xsl:text>
+    <xsl:text>            this.opened = true;
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        // Put text element in normalized state
+</xsl:text>
+    <xsl:text>        reset_text(){
+</xsl:text>
+    <xsl:text>            let txt = this.text_elt; 
+</xsl:text>
+    <xsl:text>            let first = txt.firstElementChild;
+</xsl:text>
+    <xsl:text>            // remove attribute eventually added to first text line while opening
+</xsl:text>
+    <xsl:text>            first.removeAttribute("onclick");
+</xsl:text>
+    <xsl:text>            first.removeAttribute("dy");
+</xsl:text>
+    <xsl:text>            // keep only the first line of text
+</xsl:text>
+    <xsl:text>            for(let span of Array.from(txt.children).slice(1)){
+</xsl:text>
+    <xsl:text>                txt.removeChild(span)
+</xsl:text>
+    <xsl:text>            }
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        // Put rectangle element in saved original state
+</xsl:text>
+    <xsl:text>        reset_box(){
+</xsl:text>
+    <xsl:text>            let m = this.box_bbox;
+</xsl:text>
+    <xsl:text>            let b = this.box_elt;
+</xsl:text>
+    <xsl:text>            b.x.baseVal.value = m.x;
+</xsl:text>
+    <xsl:text>            b.y.baseVal.value = m.y;
+</xsl:text>
+    <xsl:text>            b.width.baseVal.value = m.width;
+</xsl:text>
+    <xsl:text>            b.height.baseVal.value = m.height;
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>        // Use margin and text size to compute box size
+</xsl:text>
+    <xsl:text>        adjust_box_to_text(){
+</xsl:text>
+    <xsl:text>            let [lmargin, tmargin] = this.margins;
+</xsl:text>
+    <xsl:text>            let m = this.text_elt.getBBox();
+</xsl:text>
+    <xsl:text>            let b = this.box_elt;
+</xsl:text>
+    <xsl:text>            b.x.baseVal.value = m.x - lmargin;
+</xsl:text>
+    <xsl:text>            b.y.baseVal.value = m.y - tmargin;
+</xsl:text>
+    <xsl:text>            b.width.baseVal.value = 2 * lmargin + m.width;
+</xsl:text>
+    <xsl:text>            b.height.baseVal.value = 2 * tmargin + m.height;
+</xsl:text>
+    <xsl:text>        }
+</xsl:text>
+    <xsl:text>    }
+</xsl:text>
+  </xsl:template>
   <xsl:template mode="widget_defs" match="widget[@type='DropDown']">
     <xsl:param name="hmi_element"/>
     <xsl:call-template name="defs_by_labels">
@@ -3071,39 +3559,9 @@
         <xsl:text>text box button</xsl:text>
       </xsl:with-param>
     </xsl:call-template>
-    <xsl:text>    dispatch: function(value) {
-</xsl:text>
-    <xsl:text>        if(!this.opened) this.set_selection(value);
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    init: function() {
-</xsl:text>
-    <xsl:text>        this.button_elt.setAttribute("onclick", "hmi_widgets['</xsl:text>
-    <xsl:value-of select="$hmi_element/@id"/>
-    <xsl:text>'].on_button_click()");
-</xsl:text>
-    <xsl:text>        // Save original size of rectangle
-</xsl:text>
-    <xsl:text>        this.box_bbox = this.box_elt.getBBox()
-</xsl:text>
-    <xsl:text>
-</xsl:text>
-    <xsl:text>        // Compute margins
-</xsl:text>
-    <xsl:text>        text_bbox = this.text_elt.getBBox()
-</xsl:text>
-    <xsl:text>        lmargin = text_bbox.x - this.box_bbox.x;
-</xsl:text>
-    <xsl:text>        tmargin = text_bbox.y - this.box_bbox.y;
-</xsl:text>
-    <xsl:text>        this.margins = [lmargin, tmargin].map(x =&gt; Math.max(x,0));
-</xsl:text>
-    <xsl:text>
-</xsl:text>
-    <xsl:text>        // It is assumed that list content conforms to Array interface.
-</xsl:text>
-    <xsl:text>        this.content = [
+    <xsl:text>    // It is assumed that list content conforms to Array interface.
+</xsl:text>
+    <xsl:text>    content: [
 </xsl:text>
     <xsl:for-each select="arg">
       <xsl:text>"</xsl:text>
@@ -3111,467 +3569,9 @@
       <xsl:text>",
 </xsl:text>
     </xsl:for-each>
-    <xsl:text>        ];
-</xsl:text>
-    <xsl:text>
-</xsl:text>
-    <xsl:text>        // Index of first visible element in the menu, when opened
-</xsl:text>
-    <xsl:text>        this.menu_offset = 0;
-</xsl:text>
-    <xsl:text>
-</xsl:text>
-    <xsl:text>        // How mutch to lift the menu vertically so that it does not cross bottom border
-</xsl:text>
-    <xsl:text>        this.lift = 0;
-</xsl:text>
-    <xsl:text>
-</xsl:text>
-    <xsl:text>        // Event handlers cannot be object method ('this' is unknown)
-</xsl:text>
-    <xsl:text>        // as a workaround, handler given to addEventListener is bound in advance.
-</xsl:text>
-    <xsl:text>        this.bound_close_on_click_elsewhere = this.close_on_click_elsewhere.bind(this);
-</xsl:text>
-    <xsl:text>
-</xsl:text>
-    <xsl:text>        this.opened = false;
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    // Called when a menu entry is clicked
-</xsl:text>
-    <xsl:text>    on_selection_click: function(selection) {
-</xsl:text>
-    <xsl:text>        this.close();
-</xsl:text>
-    <xsl:text>        this.apply_hmi_value(0, selection);
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    on_button_click: function() {
-</xsl:text>
-    <xsl:text>        this.open();
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    on_backward_click: function(){
-</xsl:text>
-    <xsl:text>        this.scroll(false);
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    on_forward_click:function(){
-</xsl:text>
-    <xsl:text>        this.scroll(true);
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    set_selection: function(value) {
-</xsl:text>
-    <xsl:text>        let display_str;
-</xsl:text>
-    <xsl:text>        if(value &gt;= 0 &amp;&amp; value &lt; this.content.length){
-</xsl:text>
-    <xsl:text>            // if valid selection resolve content
-</xsl:text>
-    <xsl:text>            display_str = this.content[value];
-</xsl:text>
-    <xsl:text>            this.last_selection = value;
-</xsl:text>
-    <xsl:text>        } else {
-</xsl:text>
-    <xsl:text>            // otherwise show problem
-</xsl:text>
-    <xsl:text>            display_str = "?"+String(value)+"?";
-</xsl:text>
-    <xsl:text>        }
-</xsl:text>
-    <xsl:text>        // It is assumed that first span always stays,
-</xsl:text>
-    <xsl:text>        // and contains selection when menu is closed
-</xsl:text>
-    <xsl:text>        this.text_elt.firstElementChild.textContent = display_str;
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    grow_text: function(up_to) {
-</xsl:text>
-    <xsl:text>        let count = 1;
-</xsl:text>
-    <xsl:text>        let txt = this.text_elt; 
-</xsl:text>
-    <xsl:text>        let first = txt.firstElementChild;
-</xsl:text>
-    <xsl:text>        // Real world (pixels) boundaries of current page
-</xsl:text>
-    <xsl:text>        let bounds = svg_root.getBoundingClientRect(); 
-</xsl:text>
-    <xsl:text>        this.lift = 0;
-</xsl:text>
-    <xsl:text>        while(count &lt; up_to) {
-</xsl:text>
-    <xsl:text>            let next = first.cloneNode();
-</xsl:text>
-    <xsl:text>            // relative line by line text flow instead of absolute y coordinate
-</xsl:text>
-    <xsl:text>            next.removeAttribute("y");
-</xsl:text>
-    <xsl:text>            next.setAttribute("dy", "1.1em");
-</xsl:text>
-    <xsl:text>            // default content to allow computing text element bbox
-</xsl:text>
-    <xsl:text>            next.textContent = "...";
-</xsl:text>
-    <xsl:text>            // append new span to text element
-</xsl:text>
-    <xsl:text>            txt.appendChild(next);
-</xsl:text>
-    <xsl:text>            // now check if text extended by one row fits to page
-</xsl:text>
-    <xsl:text>            // FIXME : exclude margins to be more accurate on box size
-</xsl:text>
-    <xsl:text>            let rect = txt.getBoundingClientRect();
-</xsl:text>
-    <xsl:text>            if(rect.bottom &gt; bounds.bottom){
-</xsl:text>
-    <xsl:text>                // in case of overflow at the bottom, lift up one row
-</xsl:text>
-    <xsl:text>                let backup = first.getAttribute("dy");
-</xsl:text>
-    <xsl:text>                // apply lift asr a dy added too first span (y attrib stays)
-</xsl:text>
-    <xsl:text>                first.setAttribute("dy", "-"+String((this.lift+1)*1.1)+"em");
-</xsl:text>
-    <xsl:text>                rect = txt.getBoundingClientRect();
-</xsl:text>
-    <xsl:text>                if(rect.top &gt; bounds.top){
-</xsl:text>
-    <xsl:text>                    this.lift += 1;
-</xsl:text>
-    <xsl:text>                } else {
-</xsl:text>
-    <xsl:text>                    // if it goes over the top, then backtrack
-</xsl:text>
-    <xsl:text>                    // restore dy attribute on first span
-</xsl:text>
-    <xsl:text>                    if(backup)
-</xsl:text>
-    <xsl:text>                        first.setAttribute("dy", backup);
-</xsl:text>
-    <xsl:text>                    else
-</xsl:text>
-    <xsl:text>                        first.removeAttribute("dy");
-</xsl:text>
-    <xsl:text>                    // remove unwanted child
-</xsl:text>
-    <xsl:text>                    txt.removeChild(next);
-</xsl:text>
-    <xsl:text>                    return count;
-</xsl:text>
-    <xsl:text>                }
-</xsl:text>
-    <xsl:text>            }
-</xsl:text>
-    <xsl:text>            count++;
-</xsl:text>
-    <xsl:text>        }
-</xsl:text>
-    <xsl:text>        return count;
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    close_on_click_elsewhere: function(e) {
-</xsl:text>
-    <xsl:text>        // inhibit events not targetting spans (menu items)
-</xsl:text>
-    <xsl:text>        if(e.target.parentNode !== this.text_elt){
-</xsl:text>
-    <xsl:text>            e.stopPropagation();
-</xsl:text>
-    <xsl:text>            // close menu in case click is outside box
-</xsl:text>
-    <xsl:text>            if(e.target !== this.box_elt)
-</xsl:text>
-    <xsl:text>                this.close();
-</xsl:text>
-    <xsl:text>        }
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    close: function(){
-</xsl:text>
-    <xsl:text>        // Stop hogging all click events
-</xsl:text>
-    <xsl:text>        svg_root.removeEventListener("click", this.bound_close_on_click_elsewhere, true);
-</xsl:text>
-    <xsl:text>        // Restore position and sixe of widget elements
-</xsl:text>
-    <xsl:text>        this.reset_text();
-</xsl:text>
-    <xsl:text>        this.reset_box();
-</xsl:text>
-    <xsl:text>        // Put the button back in place
-</xsl:text>
-    <xsl:text>        this.element.appendChild(this.button_elt);
-</xsl:text>
-    <xsl:text>        // Mark as closed (to allow dispatch)
-</xsl:text>
-    <xsl:text>        this.opened = false;
-</xsl:text>
-    <xsl:text>        // Dispatch last cached value
-</xsl:text>
-    <xsl:text>        this.apply_cache();
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    // Set text content when content is smaller than menu (no scrolling)
-</xsl:text>
-    <xsl:text>    set_complete_text: function(){
-</xsl:text>
-    <xsl:text>        let spans = this.text_elt.children; 
-</xsl:text>
-    <xsl:text>        let c = 0;
-</xsl:text>
-    <xsl:text>        for(let item of this.content){
-</xsl:text>
-    <xsl:text>            let span=spans[c];
-</xsl:text>
-    <xsl:text>            span.textContent = item;
-</xsl:text>
-    <xsl:text>            span.setAttribute("onclick", "hmi_widgets['</xsl:text>
-    <xsl:value-of select="$hmi_element/@id"/>
-    <xsl:text>'].on_selection_click("+c+")");
-</xsl:text>
-    <xsl:text>            c++;
-</xsl:text>
-    <xsl:text>        }
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    // Move partial view :
-</xsl:text>
-    <xsl:text>    // false : upward, lower value
-</xsl:text>
-    <xsl:text>    // true  : downward, higher value
-</xsl:text>
-    <xsl:text>    scroll: function(forward){
-</xsl:text>
-    <xsl:text>        let contentlength = this.content.length;
-</xsl:text>
-    <xsl:text>        let spans = this.text_elt.children; 
-</xsl:text>
-    <xsl:text>        let spanslength = spans.length;
-</xsl:text>
-    <xsl:text>        // reduce accounted menu size according to jumps
-</xsl:text>
-    <xsl:text>        if(this.menu_offset != 0) spanslength--;
-</xsl:text>
-    <xsl:text>        if(this.menu_offset &lt; contentlength - 1) spanslength--;
-</xsl:text>
-    <xsl:text>        if(forward){
-</xsl:text>
-    <xsl:text>            this.menu_offset = Math.min(
-</xsl:text>
-    <xsl:text>                contentlength - spans.length + 1, 
-</xsl:text>
-    <xsl:text>                this.menu_offset + spanslength);
-</xsl:text>
-    <xsl:text>        }else{
-</xsl:text>
-    <xsl:text>            this.menu_offset = Math.max(
-</xsl:text>
-    <xsl:text>                0, 
-</xsl:text>
-    <xsl:text>                this.menu_offset - spanslength);
-</xsl:text>
-    <xsl:text>        }
-</xsl:text>
-    <xsl:text>        this.set_partial_text();
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    // Setup partial view text content
-</xsl:text>
-    <xsl:text>    // with jumps at first and last entry when appropriate
-</xsl:text>
-    <xsl:text>    set_partial_text: function(){
-</xsl:text>
-    <xsl:text>        let spans = this.text_elt.children; 
-</xsl:text>
-    <xsl:text>        let contentlength = this.content.length;
-</xsl:text>
-    <xsl:text>        let spanslength = spans.length;
-</xsl:text>
-    <xsl:text>        let i = this.menu_offset, c = 0;
-</xsl:text>
-    <xsl:text>        while(c &lt; spanslength){
-</xsl:text>
-    <xsl:text>            let span=spans[c];
-</xsl:text>
-    <xsl:text>            // backward jump only present if not exactly at start
-</xsl:text>
-    <xsl:text>            if(c == 0 &amp;&amp; i != 0){
-</xsl:text>
-    <xsl:text>                span.textContent = "&#x2191;  &#x2191;  &#x2191;";
-</xsl:text>
-    <xsl:text>                span.setAttribute("onclick", "hmi_widgets['</xsl:text>
-    <xsl:value-of select="$hmi_element/@id"/>
-    <xsl:text>'].on_backward_click()");
-</xsl:text>
-    <xsl:text>            // presence of forward jump when not right at the end
-</xsl:text>
-    <xsl:text>            }else if(c == spanslength-1 &amp;&amp; i &lt; contentlength - 1){
-</xsl:text>
-    <xsl:text>                span.textContent = "&#x2193;  &#x2193;  &#x2193;";
-</xsl:text>
-    <xsl:text>                span.setAttribute("onclick", "hmi_widgets['</xsl:text>
-    <xsl:value-of select="$hmi_element/@id"/>
-    <xsl:text>'].on_forward_click()");
-</xsl:text>
-    <xsl:text>            // otherwise normal content
-</xsl:text>
-    <xsl:text>            }else{
-</xsl:text>
-    <xsl:text>                span.textContent = this.content[i];
-</xsl:text>
-    <xsl:text>                span.setAttribute("onclick", "hmi_widgets['</xsl:text>
-    <xsl:value-of select="$hmi_element/@id"/>
-    <xsl:text>'].on_selection_click("+i+")");
-</xsl:text>
-    <xsl:text>                i++;
-</xsl:text>
-    <xsl:text>            }
-</xsl:text>
-    <xsl:text>            c++;
-</xsl:text>
-    <xsl:text>        }
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    open: function(){
-</xsl:text>
-    <xsl:text>        let length = this.content.length;
-</xsl:text>
-    <xsl:text>        // systematically reset text, to strip eventual whitespace spans
-</xsl:text>
-    <xsl:text>        this.reset_text();
-</xsl:text>
-    <xsl:text>        // grow as much as needed or possible
-</xsl:text>
-    <xsl:text>        let slots = this.grow_text(length);
-</xsl:text>
-    <xsl:text>        // Depending on final size
-</xsl:text>
-    <xsl:text>        if(slots == length) {
-</xsl:text>
-    <xsl:text>            // show all at once
-</xsl:text>
-    <xsl:text>            this.set_complete_text();
-</xsl:text>
-    <xsl:text>        } else {
-</xsl:text>
-    <xsl:text>            // eventualy align menu to current selection, compensating for lift
-</xsl:text>
-    <xsl:text>            let offset = this.last_selection - this.lift;
-</xsl:text>
-    <xsl:text>            if(offset &gt; 0)
-</xsl:text>
-    <xsl:text>                this.menu_offset = Math.min(offset + 1, length - slots + 1);
-</xsl:text>
-    <xsl:text>            else
-</xsl:text>
-    <xsl:text>                this.menu_offset = 0;
-</xsl:text>
-    <xsl:text>            // show surrounding values
-</xsl:text>
-    <xsl:text>            this.set_partial_text();
-</xsl:text>
-    <xsl:text>        }
-</xsl:text>
-    <xsl:text>        // Now that text size is known, we can set the box around it
-</xsl:text>
-    <xsl:text>        this.adjust_box_to_text();
-</xsl:text>
-    <xsl:text>        // Take button out until menu closed
-</xsl:text>
-    <xsl:text>        this.element.removeChild(this.button_elt);
-</xsl:text>
-    <xsl:text>        // Rise widget to top by moving it to last position among siblings
-</xsl:text>
-    <xsl:text>        this.element.parentNode.appendChild(this.element.parentNode.removeChild(this.element));
-</xsl:text>
-    <xsl:text>        // disable interaction with background
-</xsl:text>
-    <xsl:text>        svg_root.addEventListener("click", this.bound_close_on_click_elsewhere, true);
-</xsl:text>
-    <xsl:text>        // mark as open
-</xsl:text>
-    <xsl:text>        this.opened = true;
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    // Put text element in normalized state
-</xsl:text>
-    <xsl:text>    reset_text: function(){
-</xsl:text>
-    <xsl:text>        let txt = this.text_elt; 
-</xsl:text>
-    <xsl:text>        let first = txt.firstElementChild;
-</xsl:text>
-    <xsl:text>        // remove attribute eventually added to first text line while opening
-</xsl:text>
-    <xsl:text>        first.removeAttribute("onclick");
-</xsl:text>
-    <xsl:text>        first.removeAttribute("dy");
-</xsl:text>
-    <xsl:text>        // keep only the first line of text
-</xsl:text>
-    <xsl:text>        for(let span of Array.from(txt.children).slice(1)){
-</xsl:text>
-    <xsl:text>            txt.removeChild(span)
-</xsl:text>
-    <xsl:text>        }
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    // Put rectangle element in saved original state
-</xsl:text>
-    <xsl:text>    reset_box: function(){
-</xsl:text>
-    <xsl:text>        let m = this.box_bbox;
-</xsl:text>
-    <xsl:text>        let b = this.box_elt;
-</xsl:text>
-    <xsl:text>        b.x.baseVal.value = m.x;
-</xsl:text>
-    <xsl:text>        b.y.baseVal.value = m.y;
-</xsl:text>
-    <xsl:text>        b.width.baseVal.value = m.width;
-</xsl:text>
-    <xsl:text>        b.height.baseVal.value = m.height;
-</xsl:text>
-    <xsl:text>    },
-</xsl:text>
-    <xsl:text>    // Use margin and text size to compute box size
-</xsl:text>
-    <xsl:text>    adjust_box_to_text: function(){
-</xsl:text>
-    <xsl:text>        let [lmargin, tmargin] = this.margins;
-</xsl:text>
-    <xsl:text>        let m = this.text_elt.getBBox();
-</xsl:text>
-    <xsl:text>        let b = this.box_elt;
-</xsl:text>
-    <xsl:text>        b.x.baseVal.value = m.x - lmargin;
-</xsl:text>
-    <xsl:text>        b.y.baseVal.value = m.y - tmargin;
-</xsl:text>
-    <xsl:text>        b.width.baseVal.value = 2 * lmargin + m.width;
-</xsl:text>
-    <xsl:text>        b.height.baseVal.value = 2 * tmargin + m.height;
-</xsl:text>
-    <xsl:text>    },
+    <xsl:text>    ],
+</xsl:text>
+    <xsl:text>
 </xsl:text>
   </xsl:template>
   <xsl:template mode="widget_defs" match="widget[@type='ForEach']">
--- a/svghmi/widget_dropdown.ysl2	Thu Dec 10 15:48:15 2020 +0100
+++ b/svghmi/widget_dropdown.ysl2	Tue Dec 15 13:43:21 2020 +0100
@@ -1,252 +1,262 @@
 // widget_dropdown.ysl2
 
+template "widget[@type='DropDown']", mode="widget_class"{
+||
+    class DropDownWidget extends Widget{
+        dispatch(value) {
+            if(!this.opened) this.set_selection(value);
+        }
+        init() {
+            this.button_elt.onclick = this.on_button_click.bind(this);
+            // Save original size of rectangle
+            this.box_bbox = this.box_elt.getBBox()
+
+            // Compute margins
+            let text_bbox = this.text_elt.getBBox();
+            let lmargin = text_bbox.x - this.box_bbox.x;
+            let tmargin = text_bbox.y - this.box_bbox.y;
+            this.margins = [lmargin, tmargin].map(x => Math.max(x,0));
+
+            // Index of first visible element in the menu, when opened
+            this.menu_offset = 0;
+
+            // How mutch to lift the menu vertically so that it does not cross bottom border
+            this.lift = 0;
+
+            // Event handlers cannot be object method ('this' is unknown)
+            // as a workaround, handler given to addEventListener is bound in advance.
+            this.bound_close_on_click_elsewhere = this.close_on_click_elsewhere.bind(this);
+            this.bound_on_selection_click = this.on_selection_click.bind(this);
+            this.bound_on_backward_click = this.on_backward_click.bind(this);
+            this.bound_on_forward_click = this.on_forward_click.bind(this);
+            this.opened = false;
+        }
+        on_button_click() {
+            this.open();
+        }
+        // Called when a menu entry is clicked
+        on_selection_click(selection) {
+            this.close();
+            this.apply_hmi_value(0, selection);
+        }
+        on_backward_click(){
+            this.scroll(false);
+        }
+        on_forward_click(){
+            this.scroll(true);
+        }
+        set_selection(value) {
+            let display_str;
+            if(value >= 0 && value < this.content.length){
+                // if valid selection resolve content
+                display_str = this.content[value];
+                this.last_selection = value;
+            } else {
+                // otherwise show problem
+                display_str = "?"+String(value)+"?";
+            }
+            // It is assumed that first span always stays,
+            // and contains selection when menu is closed
+            this.text_elt.firstElementChild.textContent = display_str;
+        }
+        grow_text(up_to) {
+            let count = 1;
+            let txt = this.text_elt; 
+            let first = txt.firstElementChild;
+            // Real world (pixels) boundaries of current page
+            let bounds = svg_root.getBoundingClientRect(); 
+            this.lift = 0;
+            while(count < up_to) {
+                let next = first.cloneNode();
+                // relative line by line text flow instead of absolute y coordinate
+                next.removeAttribute("y");
+                next.setAttribute("dy", "1.1em");
+                // default content to allow computing text element bbox
+                next.textContent = "...";
+                // append new span to text element
+                txt.appendChild(next);
+                // now check if text extended by one row fits to page
+                // FIXME : exclude margins to be more accurate on box size
+                let rect = txt.getBoundingClientRect();
+                if(rect.bottom > bounds.bottom){
+                    // in case of overflow at the bottom, lift up one row
+                    let backup = first.getAttribute("dy");
+                    // apply lift asr a dy added too first span (y attrib stays)
+                    first.setAttribute("dy", "-"+String((this.lift+1)*1.1)+"em");
+                    rect = txt.getBoundingClientRect();
+                    if(rect.top > bounds.top){
+                        this.lift += 1;
+                    } else {
+                        // if it goes over the top, then backtrack
+                        // restore dy attribute on first span
+                        if(backup)
+                            first.setAttribute("dy", backup);
+                        else
+                            first.removeAttribute("dy");
+                        // remove unwanted child
+                        txt.removeChild(next);
+                        return count;
+                    }
+                }
+                count++;
+            }
+            return count;
+        }
+        close_on_click_elsewhere(e) {
+            // inhibit events not targetting spans (menu items)
+            if(e.target.parentNode !== this.text_elt){
+                e.stopPropagation();
+                // close menu in case click is outside box
+                if(e.target !== this.box_elt)
+                    this.close();
+            }
+        }
+        close(){
+            // Stop hogging all click events
+            svg_root.removeEventListener("click", this.bound_close_on_click_elsewhere, true);
+            // Restore position and sixe of widget elements
+            this.reset_text();
+            this.reset_box();
+            // Put the button back in place
+            this.element.appendChild(this.button_elt);
+            // Mark as closed (to allow dispatch)
+            this.opened = false;
+            // Dispatch last cached value
+            this.apply_cache();
+        }
+        // Set text content when content is smaller than menu (no scrolling)
+        set_complete_text(){
+            let spans = this.text_elt.children; 
+            let c = 0;
+            for(let item of this.content){
+                let span=spans[c];
+                span.textContent = item;
+                let sel = c;
+                span.onclick = (evt) => this.bound_on_selection_click(sel);
+                c++;
+            }
+        }
+        // Move partial view :
+        // false : upward, lower value
+        // true  : downward, higher value
+        scroll(forward){
+            let contentlength = this.content.length;
+            let spans = this.text_elt.children; 
+            let spanslength = spans.length;
+            // reduce accounted menu size according to jumps
+            if(this.menu_offset != 0) spanslength--;
+            if(this.menu_offset < contentlength - 1) spanslength--;
+            if(forward){
+                this.menu_offset = Math.min(
+                    contentlength - spans.length + 1, 
+                    this.menu_offset + spanslength);
+            }else{
+                this.menu_offset = Math.max(
+                    0, 
+                    this.menu_offset - spanslength);
+            }
+            this.set_partial_text();
+        }
+        // Setup partial view text content
+        // with jumps at first and last entry when appropriate
+        set_partial_text(){
+            let spans = this.text_elt.children; 
+            let contentlength = this.content.length;
+            let spanslength = spans.length;
+            let i = this.menu_offset, c = 0;
+            while(c < spanslength){
+                let span=spans[c];
+                // backward jump only present if not exactly at start
+                if(c == 0 && i != 0){
+                    span.textContent = "↑  ↑  ↑";
+                    span.onclick = this.bound_on_backward_click;
+                // presence of forward jump when not right at the end
+                }else if(c == spanslength-1 && i < contentlength - 1){
+                    span.textContent = "↓  ↓  ↓";
+                    span.onclick = this.bound_on_forward_click;
+                // otherwise normal content
+                }else{
+                    span.textContent = this.content[i];
+                    let sel = i;
+                    span.onclick = (evt) => this.bound_on_selection_click(sel);
+                    i++;
+                }
+                c++;
+            }
+        }
+        open(){
+            let length = this.content.length;
+            // systematically reset text, to strip eventual whitespace spans
+            this.reset_text();
+            // grow as much as needed or possible
+            let slots = this.grow_text(length);
+            // Depending on final size
+            if(slots == length) {
+                // show all at once
+                this.set_complete_text();
+            } else {
+                // eventualy align menu to current selection, compensating for lift
+                let offset = this.last_selection - this.lift;
+                if(offset > 0)
+                    this.menu_offset = Math.min(offset + 1, length - slots + 1);
+                else
+                    this.menu_offset = 0;
+                // show surrounding values
+                this.set_partial_text();
+            }
+            // Now that text size is known, we can set the box around it
+            this.adjust_box_to_text();
+            // Take button out until menu closed
+            this.element.removeChild(this.button_elt);
+            // Rise widget to top by moving it to last position among siblings
+            this.element.parentNode.appendChild(this.element.parentNode.removeChild(this.element));
+            // disable interaction with background
+            svg_root.addEventListener("click", this.bound_close_on_click_elsewhere, true);
+            // mark as open
+            this.opened = true;
+        }
+        // Put text element in normalized state
+        reset_text(){
+            let txt = this.text_elt; 
+            let first = txt.firstElementChild;
+            // remove attribute eventually added to first text line while opening
+            first.removeAttribute("onclick");
+            first.removeAttribute("dy");
+            // keep only the first line of text
+            for(let span of Array.from(txt.children).slice(1)){
+                txt.removeChild(span)
+            }
+        }
+        // Put rectangle element in saved original state
+        reset_box(){
+            let m = this.box_bbox;
+            let b = this.box_elt;
+            b.x.baseVal.value = m.x;
+            b.y.baseVal.value = m.y;
+            b.width.baseVal.value = m.width;
+            b.height.baseVal.value = m.height;
+        }
+        // Use margin and text size to compute box size
+        adjust_box_to_text(){
+            let [lmargin, tmargin] = this.margins;
+            let m = this.text_elt.getBBox();
+            let b = this.box_elt;
+            b.x.baseVal.value = m.x - lmargin;
+            b.y.baseVal.value = m.y - tmargin;
+            b.width.baseVal.value = 2 * lmargin + m.width;
+            b.height.baseVal.value = 2 * tmargin + m.height;
+        }
+    }
+||
+}
 template "widget[@type='DropDown']", mode="widget_defs" {
     param "hmi_element";
     labels("text box button");
 ||
-    dispatch: function(value) {
-        if(!this.opened) this.set_selection(value);
-    },
-    init: function() {
-        this.button_elt.setAttribute("onclick", "hmi_widgets['«$hmi_element/@id»'].on_button_click()");
-        // Save original size of rectangle
-        this.box_bbox = this.box_elt.getBBox()
-
-        // Compute margins
-        text_bbox = this.text_elt.getBBox()
-        lmargin = text_bbox.x - this.box_bbox.x;
-        tmargin = text_bbox.y - this.box_bbox.y;
-        this.margins = [lmargin, tmargin].map(x => Math.max(x,0));
-
-        // It is assumed that list content conforms to Array interface.
-        this.content = [
-        ``foreach "arg" | "«@value»",
-        ];
-
-        // Index of first visible element in the menu, when opened
-        this.menu_offset = 0;
-
-        // How mutch to lift the menu vertically so that it does not cross bottom border
-        this.lift = 0;
-
-        // Event handlers cannot be object method ('this' is unknown)
-        // as a workaround, handler given to addEventListener is bound in advance.
-        this.bound_close_on_click_elsewhere = this.close_on_click_elsewhere.bind(this);
-
-        this.opened = false;
-    },
-    // Called when a menu entry is clicked
-    on_selection_click: function(selection) {
-        this.close();
-        this.apply_hmi_value(0, selection);
-    },
-    on_button_click: function() {
-        this.open();
-    },
-    on_backward_click: function(){
-        this.scroll(false);
-    },
-    on_forward_click:function(){
-        this.scroll(true);
-    },
-    set_selection: function(value) {
-        let display_str;
-        if(value >= 0 && value < this.content.length){
-            // if valid selection resolve content
-            display_str = this.content[value];
-            this.last_selection = value;
-        } else {
-            // otherwise show problem
-            display_str = "?"+String(value)+"?";
-        }
-        // It is assumed that first span always stays,
-        // and contains selection when menu is closed
-        this.text_elt.firstElementChild.textContent = display_str;
-    },
-    grow_text: function(up_to) {
-        let count = 1;
-        let txt = this.text_elt; 
-        let first = txt.firstElementChild;
-        // Real world (pixels) boundaries of current page
-        let bounds = svg_root.getBoundingClientRect(); 
-        this.lift = 0;
-        while(count < up_to) {
-            let next = first.cloneNode();
-            // relative line by line text flow instead of absolute y coordinate
-            next.removeAttribute("y");
-            next.setAttribute("dy", "1.1em");
-            // default content to allow computing text element bbox
-            next.textContent = "...";
-            // append new span to text element
-            txt.appendChild(next);
-            // now check if text extended by one row fits to page
-            // FIXME : exclude margins to be more accurate on box size
-            let rect = txt.getBoundingClientRect();
-            if(rect.bottom > bounds.bottom){
-                // in case of overflow at the bottom, lift up one row
-                let backup = first.getAttribute("dy");
-                // apply lift asr a dy added too first span (y attrib stays)
-                first.setAttribute("dy", "-"+String((this.lift+1)*1.1)+"em");
-                rect = txt.getBoundingClientRect();
-                if(rect.top > bounds.top){
-                    this.lift += 1;
-                } else {
-                    // if it goes over the top, then backtrack
-                    // restore dy attribute on first span
-                    if(backup)
-                        first.setAttribute("dy", backup);
-                    else
-                        first.removeAttribute("dy");
-                    // remove unwanted child
-                    txt.removeChild(next);
-                    return count;
-                }
-            }
-            count++;
-        }
-        return count;
-    },
-    close_on_click_elsewhere: function(e) {
-        // inhibit events not targetting spans (menu items)
-        if(e.target.parentNode !== this.text_elt){
-            e.stopPropagation();
-            // close menu in case click is outside box
-            if(e.target !== this.box_elt)
-                this.close();
-        }
-    },
-    close: function(){
-        // Stop hogging all click events
-        svg_root.removeEventListener("click", this.bound_close_on_click_elsewhere, true);
-        // Restore position and sixe of widget elements
-        this.reset_text();
-        this.reset_box();
-        // Put the button back in place
-        this.element.appendChild(this.button_elt);
-        // Mark as closed (to allow dispatch)
-        this.opened = false;
-        // Dispatch last cached value
-        this.apply_cache();
-    },
-    // Set text content when content is smaller than menu (no scrolling)
-    set_complete_text: function(){
-        let spans = this.text_elt.children; 
-        let c = 0;
-        for(let item of this.content){
-            let span=spans[c];
-            span.textContent = item;
-            span.setAttribute("onclick", "hmi_widgets['«$hmi_element/@id»'].on_selection_click("+c+")");
-            c++;
-        }
-    },
-    // Move partial view :
-    // false : upward, lower value
-    // true  : downward, higher value
-    scroll: function(forward){
-        let contentlength = this.content.length;
-        let spans = this.text_elt.children; 
-        let spanslength = spans.length;
-        // reduce accounted menu size according to jumps
-        if(this.menu_offset != 0) spanslength--;
-        if(this.menu_offset < contentlength - 1) spanslength--;
-        if(forward){
-            this.menu_offset = Math.min(
-                contentlength - spans.length + 1, 
-                this.menu_offset + spanslength);
-        }else{
-            this.menu_offset = Math.max(
-                0, 
-                this.menu_offset - spanslength);
-        }
-        this.set_partial_text();
-    },
-    // Setup partial view text content
-    // with jumps at first and last entry when appropriate
-    set_partial_text: function(){
-        let spans = this.text_elt.children; 
-        let contentlength = this.content.length;
-        let spanslength = spans.length;
-        let i = this.menu_offset, c = 0;
-        while(c < spanslength){
-            let span=spans[c];
-            // backward jump only present if not exactly at start
-            if(c == 0 && i != 0){
-                span.textContent = "↑  ↑  ↑";
-                span.setAttribute("onclick", "hmi_widgets['«$hmi_element/@id»'].on_backward_click()");
-            // presence of forward jump when not right at the end
-            }else if(c == spanslength-1 && i < contentlength - 1){
-                span.textContent = "↓  ↓  ↓";
-                span.setAttribute("onclick", "hmi_widgets['«$hmi_element/@id»'].on_forward_click()");
-            // otherwise normal content
-            }else{
-                span.textContent = this.content[i];
-                span.setAttribute("onclick", "hmi_widgets['«$hmi_element/@id»'].on_selection_click("+i+")");
-                i++;
-            }
-            c++;
-        }
-    },
-    open: function(){
-        let length = this.content.length;
-        // systematically reset text, to strip eventual whitespace spans
-        this.reset_text();
-        // grow as much as needed or possible
-        let slots = this.grow_text(length);
-        // Depending on final size
-        if(slots == length) {
-            // show all at once
-            this.set_complete_text();
-        } else {
-            // eventualy align menu to current selection, compensating for lift
-            let offset = this.last_selection - this.lift;
-            if(offset > 0)
-                this.menu_offset = Math.min(offset + 1, length - slots + 1);
-            else
-                this.menu_offset = 0;
-            // show surrounding values
-            this.set_partial_text();
-        }
-        // Now that text size is known, we can set the box around it
-        this.adjust_box_to_text();
-        // Take button out until menu closed
-        this.element.removeChild(this.button_elt);
-        // Rise widget to top by moving it to last position among siblings
-        this.element.parentNode.appendChild(this.element.parentNode.removeChild(this.element));
-        // disable interaction with background
-        svg_root.addEventListener("click", this.bound_close_on_click_elsewhere, true);
-        // mark as open
-        this.opened = true;
-    },
-    // Put text element in normalized state
-    reset_text: function(){
-        let txt = this.text_elt; 
-        let first = txt.firstElementChild;
-        // remove attribute eventually added to first text line while opening
-        first.removeAttribute("onclick");
-        first.removeAttribute("dy");
-        // keep only the first line of text
-        for(let span of Array.from(txt.children).slice(1)){
-            txt.removeChild(span)
-        }
-    },
-    // Put rectangle element in saved original state
-    reset_box: function(){
-        let m = this.box_bbox;
-        let b = this.box_elt;
-        b.x.baseVal.value = m.x;
-        b.y.baseVal.value = m.y;
-        b.width.baseVal.value = m.width;
-        b.height.baseVal.value = m.height;
-    },
-    // Use margin and text size to compute box size
-    adjust_box_to_text: function(){
-        let [lmargin, tmargin] = this.margins;
-        let m = this.text_elt.getBBox();
-        let b = this.box_elt;
-        b.x.baseVal.value = m.x - lmargin;
-        b.y.baseVal.value = m.y - tmargin;
-        b.width.baseVal.value = 2 * lmargin + m.width;
-        b.height.baseVal.value = 2 * tmargin + m.height;
-    },
+    // It is assumed that list content conforms to Array interface.
+    content: [
+    ``foreach "arg" | "«@value»",
+    ],
+
 ||
 }