bolt/test/scan/000-bolt-identifier.md

type	expect	split-lines
scan	BoltIdentifier	true

The most simple identifiers are those made out of ASCII letters:

Foo
Bar
Baz

However, they may also contain digits as long as they do not begin with a digit:

Var1
Var2
Var10029384

Identifiers may be as long as you want:

ThisIsALongAndValidIdentifier
ThisIsAnEvenLongButStilCompletelyValidIdentifier

Moreover, they may have arbitrary underscores (_) in their names.

a_valid_identifier
another__0000__valid_identfier
_1
__2
___3

They may even be nothing more than underscores:

_
__
___

All identifiers starting with a ID_Start character are valid identifiers, including Other_ID_Start:

℘rototype
℮llipsis

Likewise, the following code points using Other_ID_Continue are also valid:

α·β
ano·teleia

And, of course, the combination of ID_Start and ID_Continue:

alfa·beta