Clarify language around the applyFor*Source functions
Clarify language around the applyFor*Source functions

The return value tells us how to generate code.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=302783377

yext/closure-templates,google/closure-templates,yext/closure-templates,google/closure-templates,google/closure-templates,google/closure-templates,google/closure-templates,yext/closure-templates,yext/closure-templates