Invokes Windows help for the required function or property:

ch.Help 'LS'        © help on linestyle
ch.Help 'Help'      © Help on this function
ctx„0 ch.Help 'ST'  © Find context# only

The optional additional argument of 0 causes it to return the context number only. This is to allow you to build context-sensitive help into your own RainPro authoring tools.