Thanks for the tip, Wayne. I've gotten template population working
using these "namespaced" section names as well, but it took some
digging!
For instance, to fill the two columns of a "1:2 columns" style
template, you must pass in "html_repeat_1:0:tiwc300_content00" and
"html_repeat_2:0:tiwc300_content01". I sorta reverse-engineered these
by cross-referencing the template preview & source. The pattern for
these repeatable section names appears to be:
[mc:repeatable]:[mc:repeatindex]:[mc:edit]