Forest: How do I automatically align tiers and have parent anchor=south

I am trying to make basic linguistic trees in Forest that do two things: 1) have the bottom leaves aligned on a single tier, and 2) have parent anchor=south. (Actually I have a third requirement as well: to be able to use line-breaks in leaves, but that's another issue.) Currently I can brute force these together by specifying the tier for each leaf as needed (fine for the occasional small tree, irritating for many or larger trees).

The Forest documentation ( http://mirrors.ibiblio.org/CTAN/graphics/pgf/contrib/forest/forest-doc.pdf ) does provide a technique for doing this alignment automatically (p. 7, ex. 12), but if I try this while also specifying parent anchor I get this error:

! Package pgfkeys Error: I do not know the key '/tikz/{parent anchor=south} whe re n children', to which you passed '0{tier=word}{}', and I am going to ignore it. Perhaps you misspelled it.

I am very new to Forest, so maybe I'm missing something obvious. Below is my MWE, first with the brute-forced version A that gives the correct output:

And this is followed by the automated version that produces the correct alignment, but without any parent anchoring specified (I've included the line the breaks it, but commented out):

I would like to be able to use an automated alignment, as in B, but with the anchoring of A. Thank you.

\documentclass[a4paper,12pt]{article}\usepackage{tikz}\usepackage{forest}\begin{document}A) Correct tree, but brute-forced:\begin{forest}{parent anchor=south}[[strong    [strong[Cant,tier=word]]    [weak[wara,tier=word]]][weak    [byrig,tier=word]]]       \end{forest}B) Automated tree, but with wrong parent anchor:\begin{forest}%{parent anchor=south}where n children=0{tier=word}{}[[strong    [strong[Cant]]    [weak[wara]]][weak    [byrig]]]   \end{forest}\end{document}