definition of children?

[bkardell]

A bunch of stuff in the spec refers to children of elements, and it looks like we even do some things in the CSS based on counts/position of children but the meaning here might be unfamilliar to me? For example in 3.4.2.1 Children of , , I am read this as that a <msubsup> with 4 children should lay out as a <mrow>, and indeed if I give it markup like this:

    <math style="display:block;">
      <mrow>
        <munderover>
          <mo>∏</mo>
          <mrow>
            <mi>j</mi>
            <mo>=</mo>
            <mn>0</mn>
          </mrow>
          <mo>f</mo>
          <mo>f</mo>
      </mrow>
    </math>

I get, nothing in ff, an error in safari, and what is described in the spec (I think) in Igalia's current Chromium fork (78.0.3898.0 r c97bb8d2d82b9c7470e8f5115f8d657d5c7f3615-refs/heads/master@{#691974})

A test for someone to confirm

but if I made the actual 3rd child have style="display:none", this appears to render as if that child doesn't exist at all - in all of the browsers... So, do I misunderstand something or are our current words just inadequate?

And the test for that should be here

[fred-wang]

This needs to be updated after we reach consensus on w3c/mathml-core#136 and #48 ; currently definitions are copied from MathML3 which only rely on the DOM tree, not on the CSS visual formatting model.

The summary is:

• MathML elements generate boxes as defined in https://www.w3.org/TR/CSS22/visuren.html#visual-model-intro
• display: none elements don't create any box per https://www.w3.org/TR/CSS22/visuren.html#propdef-display
• position: absolute elements and similar generate out-of-flow boxes https://drafts.csswg.org/css-display/#out-of-flow which are ignored for the layout of the parent.
• So for layout purposes, "children" means "in-flow chid boxes": https://drafts.csswg.org/css-display/#in-flow

There are probably some places where "children" still means children in the element tree. For example, that's always the case for CSS selectors in the UA sheets. In practice, people don't use out-of-flow or "display: none" elements so definitions will match.

[fred-wang]

This is now clarified.