The size tag was similar to the big/small tags we have now in the forums except it allowed any number
https://scratch.mit.edu/discuss/post/886/

It seems as if the size tag was removed in this commit (mirror).
The actual implementation was in postmarkup though, and can be seen here.
(don't mind me, just writing this down for later)

chipmunkmc wrote:

It seems as if the size tag was removed in this commit (mirror).
The actual implementation was in postmarkup though, and can be seen here.
(don't mind me, just writing this down for later)

It seems like we'll have to implement it manually, then. Oh well. Luckily, it's just a very simple replacement, so like [size 32] becomes <span style="font-size:32px">.

Added, will close when the update will be applied to this website.

Should be merged now.