By pressing F1, when the element’s symbol is selected.
To define a help topic ID for the DSL element
Select the appropriate customization element and open its Specification window.
In the general specification pane, select the Help ID property and type the help topic ID.
Click Close when you are done.
After updating the customization element specification, you must either reuse the DSL Customization profile in the model or reopen the model.
If an element represents two or more DSL elements, the first DSL element’s help topic ID will be taken.
If the DSL type customization does not have the Help ID property defined, the help topic ID derives from the more general stereotype customization (ancestor) of the Help ID property. If there is no ancestor, the metaclass help opens.