How does homebrew learn about software version?

[o2genum]

I see, Homebrew is aware of software versions:

$ tree -L 2 /opt/homebrew/Cellar 
/opt/homebrew/Cellar
├── autoconf
│   └── 2.69
├── bdw-gc
│   └── 8.0.4_2
├── c-ares
│   └── 1.17.1
├── gdbm
│   ├── 1.18.1_1
│   └── 1.19
├── gettext
│   └── 0.21
...

But where does it get these versions?

The Formulae seem to include:

• big versions allowing for parallel installs like python@3
• revision field

... but not the kind of version I see in the Cellar directory tree.

[SMillerDev]

It parses it from the URL or uses a version field if that fails.