================================================================================
[ExplSyntaxOn] colon/underscore is not letter
================================================================================
\bar:wibble_wobble
--------------------------------------------------------------------------------
(document
  (cs)
  (text)
  (text)
  (text))

================================================================================
[ExplSyntaxOn] colon/underscore is letter
================================================================================
\ExplSyntaxOn\bar:wibble_wobble\ExplSyntaxOff
--------------------------------------------------------------------------------
(document
  (ExplSyntaxOn (cs))
  (cs)
  (ExplSyntaxOff (cs)))

================================================================================
[ProvidesExplPackage] colon/underscore is letter
================================================================================
\ProvidesExplPackage{foo}{bar}{wibble}{wobble}
\bar:wibble_wobble
--------------------------------------------------------------------------------
(document
  (ProvidesExpl
    (cs)
    (group (l) (text) (r))
    (group (l) (text) (r))
    (group (l) (text) (r))
    (group (l) (text) (r)))
  (cs))

================================================================================
[ExplSyntaxOn] colon/underscore is letter in text group
================================================================================
\ExplSyntaxOn{\bar:wibble_wobble}\ExplSyntaxOff
--------------------------------------------------------------------------------
(document
  (ExplSyntaxOn (cs))
  (group
    (l)
    (cs)
    (r))
  (ExplSyntaxOff (cs)))

================================================================================
[ExplSyntaxOn] colon/underscore is letter in optional text group
================================================================================
\ExplSyntaxOn\usepackage[foo\bar:wibble_wobble]{foo}\ExplSyntaxOff
--------------------------------------------------------------------------------
(document
  (ExplSyntaxOn (cs))
  (use (cs)
    (brack_group
      (lbrack)
      (text)
      (cs)
      (rbrack))
    (group (l) (name) (r)))
  (ExplSyntaxOff (cs)))

================================================================================
[ExplSyntaxOn] colon/underscore is letter then other
================================================================================
\ExplSyntaxOn\bar:wibble_wobble\ExplSyntaxOff\quux:gronk_baffle
--------------------------------------------------------------------------------
(document
  (ExplSyntaxOn (cs))
  (cs)
  (ExplSyntaxOff (cs))
  (cs)
  (text)
  (text)
  (text))

================================================================================
[ExplSyntaxOn/makeatletter] Nested regions
================================================================================
\ExplSyntaxOn\foo@bar\makeatletter\gronk@baffle:quux_baz\makeatother\ExplSyntaxOff\zap@zip:nil_zil
--------------------------------------------------------------------------------
(document
  (ExplSyntaxOn (cs))
  (cs)
  (text)
  (makeatletter (cs))
  (cs)
  (makeatother (cs))
  (ExplSyntaxOff (cs))
  (cs)
  (text)
  (text)
  (text))

================================================================================
[ExplSyntaxOn/makeatletter] Interleaved regions
================================================================================
\ExplSyntaxOn\foo@bar\makeatletter\gronk@baffle:quux_baz\ExplSyntaxOff\zap@zip\makeatother
--------------------------------------------------------------------------------
(document
  (ExplSyntaxOn (cs))
  (cs)
  (text)
  (makeatletter (cs))
  (cs)
  (ExplSyntaxOff (cs))
  (cs)
  (makeatother (cs)))