The error message is
LINE 269:91: Multiple possible 'target' element-sub refs for '['a']'.
Arbitrarily chose https://html.spec.whatwg.org/multipage/links.html#attr-hyperlink-target
To auto-select one of the following refs, insert one of these lines into a <pre class=link-defaults> block:
spec:html; type:element-attr; for:a; text:target
spec:html; type:element-attr; for:area; text:target
spec:svg2; type:element-attr; text:target
<{a/target}>
but as can be seen from the provided choices, there's only one spec for which <{a/target}> makes sense. Why make me specify it?