---input---
echo "${a//["b"]/}"

---tokens---
'echo'        Name.Builtin
' '           Text.Whitespace
'"'           Literal.String.Double
'${'          Literal.String.Interpol
'a'           Name.Variable
'//['         Punctuation
'"b"'         Literal.String.Double
']/'          Punctuation
'}'           Literal.String.Interpol
'"'           Literal.String.Double
'\n'          Text.Whitespace