Here are the options I've thought about for attribute update syntax
Option 1. Certain types of html elements where the most common use case is attribute update, such as <img>, <iframe>, <input>, <link>, <object>, <param>... and <a> update the logical attribute by default.
$('<a id="target" href="http://yahoo.com"><span id="text">Yahoo</span></a>')
.weld({target:'http://google.com', text: 'Google'});
Option 2. Attribute to update is a configuration option
var config = {setattr: {a: 'href'}};
$('<a id="target" href="http://yahoo.com"><span id="text">Yahoo</span></a>')
.weld({target:'http://google.com', text: 'Google'}, config);
Option 3. Attribute to update is indicated in the HTML.
$('<a id="target" data-weld-attr="href" href="http://yahoo.com">' +
'<span id="text">Yahoo</span></a>')
.weld({target:'http://google.com', text: 'Google'});
Option 4. Attribute to update is indicated in the data object. (the '$' is a placeholder for the attribute separator character)
$('<a id="target" href="http://yahoo.com">Yahoo</a>')
.weld({target$href:'http://google.com', target: 'Google'});
I would prefer not to create a microlanguage here.. the other option is to use map/alias :)