Do you mean why the individual file names aren't quoted?

You can see an example config file at the bottom of that link you attached - agreed we should probably make it more obvious

heh, I don't need an example in the docs, the whole repo is filled with examples, but unless you expect some poor soul to do $(grep -r ^include . | sort | uniq) and guess from there, what I'm saying in that the examples -- including the bare bones one in your documentation -- do not SPECIFY what the glob syntax is. The good thing about standards is that there are so many to choose from, so: python's os.glob, golang's glob, I'm sure rust-lang has one, bash, ... I'm sure I could keep going

As for the quoting part, it's mysterious to me why a structured file would use a quoted string for what is obviously an interior structure. Imagine if you opened a file and saw

  fred = "{alpha: ['beta', 'charlie''s dog', 'delta']}"

wouldn't you strongly suspect that there was some interior syntax going on there?

Versus the sane encoding of:

  fred:
    alpha:
    - beta
    - charlie's dog
    - delta

in a normal markup language, no "inner/outer quoting" nonsense required

But I did preface it with my toml n00b-ness and I know that the toml folks believe they can do no wrong, so maybe that's on purpose, I dunno