“Collecting Cycles” does not accurately explain the algorithm

[TimWolla]

https://www.php.net/manual/en/features.gc.collecting-cycles.php

As discussed in PHPC Discord:

So the color “grey” guards whether the refcounts of the children were already decreased, not whether the refcount of the zval itself were decreased. That's the missing piece in the PHP explanation.

(https://discord.com/channels/356354025865740288/862784909922795600/1338911678859051088 + previous messages for context)