VANILLA_HANDLEBARS.md

During the template printing rewrite, we removed support for two kinds of vanilla Handlebars APIs:

• Some Ember enhancements, such as SomeView -> {{view SomeView}} are now always performed.
• Some Ember-specific APIs, such as p class=isEnabled:active:disabled had fallbacks to Handlebars-safe versions. Those fallbacks were removed.

To re-introduce support for vanilla Handlebars, our proposal is that the AST should be enhanced to support these syntaxes explicitly. Once that happens, a seperate vanilla template compiler can be added that ouputs vanilla syntax or raises errors as is appropriate.