[Ur] Thoughts on <meta> tags in Ur/Web?

[Adam Chlipala]

Someone recently requested a nice way to include a <meta name="viewport" 
content="..."> tag in Ur/Web.  It doesn't seem safe to expose <meta> in 
its most general form, with type [string] for each attribute, since it 
seems like browsers could interpret those strings in quite arbitrary 
ways, which goes against Ur/Web's philosophy about implicit 
interpretation of strings as programs.

Are there any opinions, then, on the right way to expose this tag?

My first thought is to add an application-level whitelist of which 
<meta> names are allowed, just as with HTTP header names. Then the 
'content' attribute could be exposed as [string], while the 'name' 
attribute would have an abstract type of allowable names. The programmer 
would need to be careful not to whitelist names that can lead to mayhem.