Hello folks! You may be familiar with the work around the <template> element, or a way to declare document fragments in HTML (see http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2011-November/033868.html for some background).
In trying to understand how this newfangled beast would work, I started researching HTML parsing, and--oh boy was I ever sorry! Err.. I mean.. --and investigating how the contents of the <template> element could be parsed. So far, I have two ideas. Both introduce changes to HTML parsing algorithm. Both have flaws, and I thought the best thing to do would be to share the data with the experts and seek their opinions. Those of you cc'd -- you're the designated experts :) == IDEA 1: Keep template contents parsing in the tokenizer == PRO: if we could come up with a way to perceive the stuff between <template> and </template> as a character stream, we enable a set of use cases where the template contents does not need to be a complete HTML subtree. For example, I could define a template that sets up a start of a table, then a few that provide repetition patterns for rows/cells, and then one to close out a table: <template id="head"><table><caption>Nyan-nyan</caption><thead> ... <tbody></template> <template id="row"><tr><template><td> ... </td></template></tr></template> <template id="foot"></tbody></table></template> Then I could slam these templates together with some API and produce an arbitrary set of tables. PRO: Since the template contents are parsed as string, we create opportunities for performance optimizations at the UA level. If a bunch of templates is declared, but only a handful is used, we could parse template contents on demand, thus reducing the churn of DOM elements. CON: Tokenizer needs to be really smart and will start looking a lot like a specialized parser. At first glance, <template> behaves much like a <textarea> -- any tags inside will just be treated as characters. It works until you realize that templates sometimes need to be nested. Any use case that involves building a larger-than-one-dimensional data representation (like tables) will involve nested templates. This makes things rather tricky. I made an attempt of sketching this out here: http://dvcs.w3.org/hg/webcomponents/raw-file/a28e16cc4167/spec/templates/index.html#parsing. As you can see, this adds a largish set of new states to tokenizer. And it is still incomplete, breaking in cases like <template><script>alert('<template> is awesome!');</script></template>. It could be argued that--while pursuing the tokenizer algorithm perfection--we could just stop at some point of complexity and issue a stern warning for developers to not get too crazy, because stuff will break -- akin to including "</script>" string in your Javascript code. == IDEA 2: Just tweak insertion modes == PRO: It's a lot less intrusive to the parser -- just adjust insertion modes to allow <template> tags in places where they would ordinary be ignored or foster-parented, and add a new insertion for template contents to let all tags in. I made a quick sketch here: http://dvcs.w3.org/hg/webcomponents/raw-file/c96f051ca008/spec/templates/index.html#parsing (Note: more massaging is needed to make it really work) CON: You can't address fun partial-tree scenarios. Which idea appeals to you? Perhaps you have better ideas? Please share. :DG<
