\foo bar
\foo:bar
\ and\
bar\foo:baz
\!!
\^^3abc
\^^3ABC
\^^xyz
% ° does not qualify for the ^^ syntax, as it is not in ASCII
\^^°!

% @ is always treated as a letter
\@foo
\foo@bar
\@ifnextchar[\@foo\@@foo

% expl3 macros are recognized
\cs_new:Nn \hljs_test:N \__hljs_internal:Nx
\use_ii_i:nn
\cs:w hljs_test:N\cs_end:
\use_i:nn \use:\q_test
\if:w\scan_stop:\s_test[\else:]\fi:
\hbox:n \vbox:n
\::c\::o\::V\:::\hljs_test_args:Nnn
\::V_unbraced
\l_hljs_var_tl \g_tmpa_prop \c__hljs_secret_int
\c_e_fp
% but only those conforming to the naming scheme with at least two letters
% in module, function, type, quark and scan mark names
% see latex.js for details
\hljs_error:Nn_foo \hljs_double:colon:x
\a:n \foo:n \x_foo:nn \foo_x:nnn
\hljs_trailing_:N \hljs__double:N \hljs_later__double:N
\::xy \::n_unbraceddd
\l_tl \c_x_int \h_imaginary_scope
\g_hljs_trailing_ \l_hljs_double__int