Above, the WHILE keyword is selected. If you now press the F1 key, then the Reference window will display a help page pertinent to use of that keyword.
Adding your own keyword help
You can easily extend Rexx Center's built-in list of recognized keywords and function names, and add new keywords and function names. And you can then create your own help pages for those new keywords/functions. One of your help pages will be displayed in the Reference window whenever one of those new keywords or function names is selected, and you press the F1 key.
You can also change the contents of the Reference, adding new pages from text files, or HTML files, or jpeg files, or anything else a browser can display.
Selecting the "Help -> Configure" menu item brings up the Reference/Keyword editor. This dialog lets you add or remove various books to the Table of Contents window, and add/remove keywords.