In the calling method of the custom (or form, or whatever) class:

DO FORM Myform WITH This

or:

loForm = CreateObject("MyForm", This)
loForm.Show()

or:

This.oForm = CreateObject("MyForm", This)
This.oForm.Show()

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In the Init of the MyForm class:

LPARAMETERS toCallingObject

Thisform.oCallingObject = toCallingObject

At this point, any method in MyForm can address any public property or method in the calling object as Thisform.oCallingObject.PropertyName or Thisform.oCallingObject.MethodName(). Note that the property or method addressed must be public.