Classic F1 Help
You can use the F1 help feature (as used on the SAP GUI) for UI elements. To do this, the relevant data element documentation must already exist in the system, and the content element concerned must be connected to an ABAP dictionary field with F1 help.
Then you can call this help up by choosing More Field Help in the context menu. The documentation from the system is then displayed.

Data element documentation example in a Web Dynpro ABAP application:

More Information:
Documentation
Maintenance Action
Overview of
Documentation Maintenance