Translatable text in tag attributes

The BL2 compiler in Jamaica treats all template text nodes as 
translatable. This means that there is no need to signal translateble 
text through <xar:mlstring> tags. Well and good.

The other place we often encounter translatable text is in certain tag 
attributes. Consider the following example:

     A. <input type="submit" value="#xarML('Log In')#" />

What can we do to simplify this construct, similar to what has been done 
in text nodes?

Here are 2 other ways of expressing the same example:

     B. <input type="submit" value="Log In" />

     C. <xar:var name="label">Log In</xar:var>
        <input type="submit" value="#$label#" />

Ideally I would like to replace A with B or C. In fact, I would pretty 
much like to remove all xarML constructs from templates and have the 
translation issue be handled in the background without any signaling.

Variant C is a cheap (implementation-wise) solution: it reduces our 
issue to an application of the text node translation already 
implemented, without any further fuss. Its drawback is that it is a bit 
less readable and a slightly more complicated construct.

Variant B looks great, until you realize that setting up a simple rule 
like "all text in attributes is translatable" would mean the name of the 
button in that example would also be translated. Probably not what we want.

Opinions?