A relative pronoun is a °relativizer that can carry a °flag or has distinct forms for the roles °A and °P.
Relativizers sometimes show gender or number distinctions reflecting the gender/number of the head noun, as in Standard Arabic, but do not carry a flag or distinguish syntactic roles. Such relativizers are not regarded as relative pronouns. (Cf. Comrie & Kuteva (2005: 494): "Note that the mere presence of a pronoun that is restricted to relative clauses, and is thus in some intuitive sense a relative pronoun, is not sufficient to define an instance of the pronoun strategy (Comrie 1998: 61-62). Such a relative pronoun can be case-marked, for instance, not to indicate its role in the relative clause, but rather to agree in case with the head noun in the main clause.")
relative pronoun (CXN) = a pronoun form that is unique to the relative clause construction, and is found in the externally headed relative clause construction using the relative pronoun strategy. Example: in He stole the emerald [which he gave to his wife], which is the relative pronoun. (Section 19.2.2)
Comrie & Kuteva (2005: 494) “[T]he position relativized is indicated inside the relative clause by means of a clause-initial pronominal element, and this pronominal element is case-marked (by case or by an adposition) to indicate the role of the head noun within the relative clause.” (http://wals.info/chapter/122) ///
Michaelis et al. (2013) "a relative-clause marker is regarded as a relative pronoun if it has different subject and object forms ..., or if it can be combined with an adposition" (http://apics-online.info/parameters/92.chapter.html).