Make default template engine less forgiving about html parsing.

[theengineear]

It’s common to leverage something like setHTMLUnsafe to let the browser parse arbitrary markup. However, this has to be incredibly forgiving as it needs to consider all current (and historic!) use cases. In general, the default template engine is not meant to serve such broad requirements. As such, it’s possible that it could benefit from significantly reducing it’s scope of concern — i.e., being less forgiving.

Some potential wins:

• Tighten control over things like double-quotes & closing tags.
• Improve error messaging for malformed markup.
• Improve performance.