Multiple dynamic placeholders in one component don't work unless they are named as column or row

[gitvadim]

Description

Looks like this PR introduced a very 'interesting' change effectively preventing the Placeholder component from rendering multiple dynamic placeholders within one component unless they are named to match a very strict regex:

What was the justification for this change? How do I go about implementing something similar to a Column or RowSplitter without naming my placeholders row or column? Not that this is a big deal, but I'm interested in knowing.

Additional information

No response

[ambrauer]

Hey @gitvadim This came up as an issue as well, and I believe should be resolved with this PR. This will go out with the next release (21.7.0, which is coming out shortly).