I've been looking at the database file of WALS that one can get at

and I have found several features that are not described in the chapter
texts anywhere:

81B. Languages with two dominant orders of subject, object, and verb
63 langs
    SOV or SVO: 26 langs
    SVO or VSO: 13 langs
    VSO or VOS: 13 langs
    SVO or VOS: 8 langs
    SOV or OVS: 3 langs

90B. Prenominal relative clauses
187 langs
    Relative clause-Noun (RelN) dominant: 139 langs
    RelN or NRel: 29 langs
    RelN or internally-headed: 15 langs
    RelN or correlative: 3 langs
    RelN or double-headed: 1 lang

90C. Postnominal relative clauses
613 langs
    Noun-Relative clause (NRel) dominant: 574 langs
    NRel or RelN: 29 langs
    NRel or internally-headed: 8 langs
    NRel or correlative: 2 langs

90D. Internally-headed relative clauses
59 langs
    Internally-headed relative clause dominant: 20 langs
    Internally-headed or RelN: 15 langs
    Internally-headed or NRel: 8 langs
    Internally-headed or correlative: 1 lang
    Internally-headed or double-headed: 1 lang
    Internally-headed occurs as nondominant type: 10 langs
    Internally-headed exists: 4 langs

90E. Correlative relative clauses
19 langs
    Correlative relative clause dominant: 7 langs
    Correlative or RelN: 3 langs
    Correlative or NRel: 2 langs
    Correlative or internally-headed: 1 lang
    Correlative or adjoined: 2 langs
    Correlative as nondominant type: 3 langs
    Correlative exists: 1 lang

90F. Adjoined relative clauses
10 langs
    Adjoined relative clause dominant: 8 langs
    Adjoined or correlative: 2 langs

90G. Double-headed relative clauses
4 langs
    Double-headed dominant: 1 lang
    Double-headed or RelN: 1 lang
    Double-headed or internally-headed: 1 lang
    Double-headed as nondominant type: 1 lang

Food for thought.