[HTML5] [html] Elements within "title"?

[Lachlan Hunt]

James Justin Harrell wrote:
> Why not create an attribute for the title element to allow markup?
> 
> <title allowmarkup="true">H<sub>2</sub>0</title>

In the HTML5 parsing algorithm, that would require the tree construction 
phase to set the content model flag in the tokeniser to RCDATA or PCDATA 
based on the presence of the attribute.  Although it might be possible 
to implement, no-one has yet given a valid use case that requires the 
use of markup in the title, is worth the cost of implementation and 
backwards imcompatibility, and has some real practical benefit for users 
and/or user agents.

Your example can be handled using:

   <title>H&#x2082;O</title>

(U+2082 is SUBSCRIPT TWO)

Or simply accept the small limitation and write:

   <title>H2O</title>

-- 
Lachlan Hunt
http://lachy.id.au/