---input---
<?php
${'whatever'} = '';
${$whatever} = '';
${${'whatever' . 'whatever'}} = '';

---tokens---
'<?php'       Comment.Preproc
'\n'          Text

'${'          Name.Variable
"'whatever'"  Literal.String.Single
'}'           Name.Variable
' '           Text
'='           Operator
' '           Text
"''"          Literal.String.Single
';'           Punctuation
'\n'          Text

'${'          Name.Variable
'$whatever'   Name.Variable
'}'           Name.Variable
' '           Text
'='           Operator
' '           Text
"''"          Literal.String.Single
';'           Punctuation
'\n'          Text

'${'          Name.Variable
'${'          Name.Variable
"'whatever'"  Literal.String.Single
' '           Text
'.'           Operator
' '           Text
"'whatever'"  Literal.String.Single
'}'           Name.Variable
'}'           Name.Variable
' '           Text
'='           Operator
' '           Text
"''"          Literal.String.Single
';'           Punctuation
'\n'          Text
