[css-grid] Base sizes and growth limits are lengths

[Loirooriol]

From https://drafts.csswg.org/css-grid/#extra-space, "Distribute space beyond growth limits":

• when handling min-content or auto base sizes [...]
• when handling max-content base sizes [...]
• when handling any intrinsic growth limit [...]

However, both base sizes and growth limits are <length>s:

Each track has a base size, a <length> which grows throughout the algorithm and which will eventually be the track’s final size, and a growth limit, a <length> which provides a desired maximum size for the base size.

I suspect it refers to the track sizing functions of the tracks that own the base sizes or growth limits. However, the tracks in the considered set may have different track sizing functions, so it doesn't make much sense to me.

[Loirooriol]

In https://drafts.csswg.org/css-grid/#algo-init there is also

Use an initial growth limit of infinity.

[Loirooriol]

So my understanding was correct, but filed follow-up #3621.

About "Use an initial growth limit of infinity", infinity is not a length, right? Are growth limits really lengths? Extended lengths?