<svg:use/> allows for infinite reference cycles.

[george-steel]

Under #UseElement, the text

If the referenced element is a (shadow-including) ancestor of the ‘use’ element, then this is an invalid circular reference and the ‘use’ element is in error.

requires the generation of infinitely deep shadow trees if it references something containing a reference cycle. It should be corrected to

If the referenced element is a (shadow-including) ancestor of the ‘use’ element or the referenced element of such an ancestor, then this is an invalid circular reference and the ‘use’ element is in error.

[AmeliaBR]

I'm not sure I understand the distinction between those two statements, if we take “shadow-including” to include the shadow trees generated by use references.

Can you give a short example code snippet that shows the problem?

[george-steel]

<svg>
  <defs>
    <g id="a">
      <rect x="10" y="10" width="50" height="50" fill="red"/>
      <use href="#b" x="60"/>
    </g>
    <g id="b">
      <rect x="10" y="10" width="50" height="50" fill="green"/>
      <use href="#c" x="60"/>
    </g>
    <g id="c">
      <rect x="10" y="10" width="50" height="50" fill="blue"/>
      <use href="#a" x="60"/>
    </g>
  </defs>
  <use href="#a"/>
</svg>

(also on codepen)

In the shadow copy of #c, #a is not an ancestor but a copy of it is.

[AmeliaBR]

Oh, I see. I would word this as:

If the referenced element, or a cloned instance of the referenced element, is a (shadow-including) ancestor of the ‘use’ element, then this is an invalid circular reference and the ‘use’ element is in error.

Do you think that would address your concerns?

[george-steel]

Yes it does. Thanks for the improvement.