html.tag() should accept multiple content items, inline

[towerofnix]

See previous discussion (#code-quarantine). This is re: addressing the following code sample.

What's this about??

Old:

html.tag('li',
  html.tag('details',
    html.isBlank(slots.items) &&
      {open: true},

    [
      html.tag('summary',
        html.tag('span',
          language.$(capsule, {
            title:
              html.tag('span', {class: 'group-name'},
                slots.title),
          }))),

      html.tag('ul', [
        html.tag('li', {class: 'entry-description'},
          {[html.onlyIfContent]: true},
          slots.description),

        (html.isBlank(slots.items)
          ? html.tag('li',
              language.$(capsule, 'noFilesAvailable'))
          : slots.items),
      ]),
    ])),

New:

html.tag('li',
  html.tag('details',
    html.isBlank(slots.items) &&
      {open: true},

    html.tag('summary',
      html.tag('span',
        language.$(capsule, {
          title:
            html.tag('span', {class: 'group-name'},
              slots.title),
        }))),

    html.tag('ul',
      html.tag('li', {class: 'entry-description'},
        {[html.onlyIfContent]: true},
        slots.description),

      (html.isBlank(slots.items)
        ? html.tag('li',
            language.$(capsule, 'noFilesAvailable'))
        : slots.items)))),

The only difficulty here is disambiguating which items are attributes and which are content. We came up with a "simple" chunk of code that does that:

It works, but it fails at the one point that html.tag() cannot solve on its own: templates whose content resolves to attributes. (For example, generateColorStyleAttribute.) In the algorithm above, "looks like attributes" simply rules that templates are never attributes. This is "fine" as an existing condition which checks the last argument to tag(), but in this context it breaks templates from ever working as attributes. And most templates are content, not attributes, so we can't just rule the other way (templates are never content—lol).

We need html.tag()—and Tag objects themselves, or at least the representative thing which html.tag() returns—to store provided arguments as-is (or "flattened" leaving templates in-place and as-is), for lazy evaluation later, when content is being stringified or otherwise processed. In other words, this most certainly depends on #331, but also extends that principle to the entire argument list for tag().

See also today discussion (#code-quarantine).