From the introduction: "A central claim of relational grammar (Perlmutter and Postal 19831, 198c, in press) is that sentences often involve more than one syntactic level. In this respect, relational grammar differs most notably from the majority of other current syntactic frameworks. We present evidence from Sierra Popoluca, a Mixe-Zoque language of Veracruz, Mexico, in support of this claim. The central evidence involves what has been called Possessor Ascension. The constructions for which we claim multilevel analyses are necessary are those which involve advancements to direct object, and Passive."
Elson, Benjamin F. and Marlett, Stephen A.
"Popoluca evidence for syntactic levels,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 27, Article 3.
Available at: https://commons.und.edu/sil-work-papers/vol27/iss1/3