Conditional attribute-assignment has changed?

[CrawfishPress]

It appears that the conditional-binding operator has changed from ?= to $=. Oddly, I can't even find conditional as a term in the current documentation https://www.polymer-project.org/1.0/docs/devguide/data-binding, but it does show the dollar-sign usage at one point. When I switched to dollar-sign in my code, it worked properly.

(Also, line 26 with the conditional-binding documentation, no longer exists).