Support existing values in the markup as defaults

[garthbongers]

One lacking feature in HTL that I enjoyed from the Zope Template Attribute Language (TAL) is the ability to fallback to default values already set in the markup.

This would enable the existing markup (whether they're element names or attribute values or other content) to be preserved should an HTL expression evaluate to a decision of inaction. The TAL approach is to use the default keyword.

For example:

• <h1 data-sly-element="${ someCondition ? 'h2' : default}">Text</h1> - would see the tag name being left alone should the condition fail
• <span class="abc" data-sly-attribute.class="${someClass || default}"></span> - would see the class attribute being preserved should someClass evaluate to false.
• <div id="myDiv" data-sly-text="${someNewContent || default}">Some <b>default</b> content</div>- would see the existing markup in #myDiv kept intact should someNewContent evaluate to false.

Maybe all of this is already doable, and I've simply overlooked it?

Thank you!

[vladbailescu]

There's no similar concept to the default keyword. But you can still do all of these with the current spec, you just need to explicitly state the default value.

• <h1 data-sly-element="${ someCondition ? 'h2' : 'h1'}">Text</h1> replaces h1 with h2 only if someCondition is true. In the current (Sling) implementation you can also use ${ someCondition ? 'h2' : ''} but the spec says the element name is required.

• <span class="abc" data-sly-attribute.class="${someClass || 'abc'}"></span> works, you could condense it to <span data-sly-attribute.class="${someClass || 'abc'}"></span>

• <div id="myDiv" data-sly-text="${someNewContent || 'Some <b>default</b> content' @ context='html'}">Some <b>default</b> content</div> works, you could also add i18n to the expression. You can shorten this to <div id="myDiv" data-sly-text="${someNewContent || 'Some <b>default</b> content' @ context='html'}"></div>