---input---
\documentclass{article}

% Comment

\ExplSyntaxOn
    \@@_command:nTF { a } { b } { c }
\ExplSyntaxOff

\makeatletter
\def\example@command{example}
\makeatother

\begin{document}

text \LaTeX: text \

text \example{}[] text \\

text \example text. ``quote''; \123\% and: text.

$\alpha_i\in\{\alpha:\alpha\leq3\}\ \text{something}$

\end{document}

---tokens---
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'{'           Name.Builtin
'article'     Text
'}'           Name.Builtin
'\n\n'        Text

'% Comment\n' Comment

'\n'          Text

'\\ExplSyntaxOn' Keyword
'\n    '      Text
'\\@@_command:nTF' Keyword
' '           Text
'{'           Name.Builtin
' a '         Text
'}'           Name.Builtin
' '           Text
'{'           Name.Builtin
' b '         Text
'}'           Name.Builtin
' '           Text
'{'           Name.Builtin
' c '         Text
'}'           Name.Builtin
'\n'          Text

'\\ExplSyntaxOff' Keyword
'\n\n'        Text

'\\makeatletter' Keyword
'\n'          Text

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'\\example@command' Keyword
'{'           Name.Builtin
'example'     Text
'}'           Name.Builtin
'\n'          Text

'\\makeatother' Keyword
'\n\n'        Text

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'{'           Name.Builtin
'document'    Text
'}'           Name.Builtin
'\n\ntext '   Text
'\\LaTeX:'    Keyword
' text '      Text
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'\n\ntext '   Text
'\\example'   Keyword
'{'           Name.Builtin
'}'           Name.Builtin
'[] text '    Text
'\\\\'        Keyword
'\n\ntext '   Text
'\\example'   Keyword
" text. ``quote''; " Text
'\\1'         Keyword
'23'          Text
'\\%'         Keyword
' and: text.\n\n' Text

'$'           Literal.String
'\\alpha'     Name.Variable
'_'           Name.Builtin
'i'           Name.Builtin
'\\in'        Name.Variable
'\\{'         Name.Variable
'\\alpha'     Name.Variable
':'           Name.Builtin
'\\alpha'     Name.Variable
'\\leq'       Name.Variable
'3'           Literal.Number
'\\}'         Name.Variable
'\\'          Name.Variable
' '           Name.Builtin
'\\text'      Name.Variable
'{'           Name.Builtin
'something'   Name.Builtin
'}'           Name.Builtin
'$'           Literal.String
'\n\n'        Text

'\\end'       Keyword
'{'           Name.Builtin
'document'    Text
'}'           Name.Builtin
'\n'          Text