3.146 pronouns as complements

Personal pronouns are sometimes used as complements to indicate identity. Note that the object pronouns are used, except in very formal speech or writing.

• It's me again.

Possessive pronouns are also used as complements, to indicate identity or to describe.

• This one is yours.
• This place is mine.

Indefinite pronouns are sometimes used to describe, usually with a qualifying structure after them.

• It's nothing serious.
• You're someone who does what she wants.

Pronouns are usually used as complements after 'be'.