Problem/Motivation
Part of #2649768: [meta] No definition of "Experimental"& not nearly enough warning. Site builders using experimental modules might struggle with troubleshooting or understanding the functionality of experimental modules, or with understanding why their help information is not complete.
Proposed resolution
Display a warning on the module help page when the module is experimental.
Remaining tasks
Patch needs review. Also see note in #3 about a potential followup.
User interface changes
Experimental modules display a warning message on their help page.
API changes
N/A
Data model changes
N/A