What is the grammatical form and function of the "needed" here and how do we know when to use this form?
This is a matter of omitting "which is" at the beginning of a relative clause. basic information (which is) needed in order to ... You can use this abbreviated construction whenever you have a relative clause that starts with "which" or "who" followed by a form of be ( am, is, are, was, were ) and a participle.
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This is a matter of omitting "which is" at the beginning of a relative clause.
... basic information (which is) needed in order to ...
You can use this abbreviated construction whenever you have a relative clause that starts with "which" or "who" followed by a form of be (am, is, are, was, were) and a participle.
the man who is walking into the bank