[whatwg] Use cases for data templates?

[Henri Sivonen]

I started reviewing data templates to assess the impact on my  
conformance checker work. Here are some questions and comments about  
data templates in general:

  * What's the use case for data templates? It is hard to review them  
without knowing what they are for. Conjecture-based comments/ 
questions follow.

  * If data templates are a replacement for WF2 repetition templates,  
they look like a harder-to-understand overkill.

  * Simple declarative markup templating mechanisms have a tendency  
to either severely limit what you can do or have a tendency to grow  
into awkward programming languages (like XSLT). Both end up being  
worse than doing straight DOM scripting with JavaScript. Is there a  
plan to avoid these usual tendencies?

  * It seems to me that data templates do not do a lot of things. Is  
there a clean way to escape to JS without having to take out data  
templates from a Web app UI and reimplementing the whole thing  
straight in JS.

  * What's the relationship with XBL2 tree adornments?

  * Markup templating on the server side is far from being a solved  
problem with a single right dominant design even though the templates  
don't need to re-evaluate on dynamic changes. Is now the right time  
to lock down one solution for clients when the server side hasn't  
settled? (Aside: My understanding is that the state of the art in  
markup templating is compiling an XML template into executable Python  
byte code that calls Python code written using the normal Python  
syntax. So far, I haven't seen declarative approaches that weren't bad.)

  * Is there a reason why querySelector() and E4X tree literals  
together don't solve what data templates seek to solve?

  * It seems to me that all non-trivial inline template uses are  
severely incompatible with HTML parsing (especially in legacy UAs).  
Is there a reason why inline templates won't break after all? If not,  
why bother with inline at all?

  * External templates seem create a new kind of busy state that DOM  
building and scripting needs to interact with. Do we really want that?

-- 
Henri Sivonen
hsivonen at iki.fi
http://hsivonen.iki.fi/