Add attribute from template engine

[Maxim Reznik]

We need a new construction in template engine to add (or delete?) new attribute of some XML/HTML element.

For instance we have <fieldset> and we want to convert it to <fieldset disabled> if some condition is met. Setting disabled="false" doesn't work, dut to value of attribute doesn't matter in HTML.

The construction could look like:

<mtl:attribute name="disabled">value</mtl:attribute>

[Maxim Reznik]

In genshi ​https://pythonhosted.org/Genshi/xml-templates.html#id6:

<ul>
  <li py:attrs="foo">Bar</li>
</ul>

Given foo={'class': 'collapse'} in the template context, this would produce:

<ul>
  <li class="collapse">Bar</li>
</ul>

[Maxim Reznik]

Genshi approach doesn't help me, because I need conditional attribute.

Another idea is to define new 'set of attributes' with name mtl:boolean-*:

<fieldset mtl:boolean-disabled="${boolean-expr}">

Evaluation of this will add attribute 'disabled=disabled' or no attribute depending on boolean-expr.

[Maxim Reznik]

In 5655:

Implement mtl:boolean.xxx="bool-expr" attribute

in XML template processor to support HTML boolean attributes.
Refs #462

[vadim.godunko]

Milestone renamed

[vadim.godunko]

Ticket retargeted after milestone closed