Customization options:  undefinedResult provider '???', pipeNotFound handler

It is confusing to become '???' as default result if value not found in context.
My use case scenario is the next:
  I process templates in more steps to generate UI and documents e.g.:

preprocessing:
   1. include other templates
   2. replace message placeholders (i18n) 
   3. cache the preprocessed tempalte

fill with model values
   4. fill the templates with model values

PS:  Mark.up rocks!