This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
The xml:space and xml:base attributes have effects in documents parsed as XML but do not have effects in documents parsed as text/html. The HTML5 spec therefore defines them as invalid in text/html documents.
xml:space and xml:base are OK on SVG and MathML elements.
Added section 7.1 to spec: 7.1 Disallowed Attributes The following attributes are not allowed in polyglot markup. These attributes have effects in documents parsed as XML but do not have effects in documents parsed as text/html. The HTML5 spec therefore defines them as invalid in text/html documents. [HTML5] xml:space xml:base Thanks for the feedback!
Also added a note: Note that the xml:space and xml:base attributes are allowed on SVG and MathML elements.