Deprecation Guide for render helper with block

The {{render}} helper was never intended to support a block form, but unfortunately (mostly due to various refactorings in 1.10 and 1.13) it started working in block form. Since this was not properly engineered, there are a number of caveats (i.e. the controller and target values of anything inside the block are incorrect) that prevent continued support.

Support the following forms will be removed after 2.4:

{{#render 'foo'}}
  <p>Stuff Here</p>
{{/render}}

{{#render 'foo' someModel}}
  <p>Stuff Here</p>
{{/render}}