According to the Wikipedia page for African-American Vernacular English:
- Only the forms is and are (of which the latter is anyway often replaced by is) can be omitted; am, was, and were are not deleted.
- These forms cannot be omitted when they would be pronounced with stress in General American (whether or not the stress serves specifically to impart an emphatic sense to the verb's meaning).
- These forms cannot be omitted when the corresponding form in standard English cannot show contraction (and vice versa). For example, I don't know where he is cannot be reduced to *I don't know where he just as in standard English forms the corresponding reduction *I don't know where he's is likewise impossible. (I don't know where he at is possible, paralleling I don't know where he's at in standard English.)
Are there any exceptions to this rule?