src/Fixer/StringNotation/ExplicitStringVariableFixer.php
private function isStringPartToken(Token $token)
    {
        return $token->isGivenKind(T_ENCAPSED_AND_WHITESPACE)
            || $token->isGivenKind(T_START_HEREDOC)
            || '"' === $token->getContent()
            || 'b"' === strtolower($token->getContent())
        ;
    }
private function isStringPartToken(Token $token)
    {
        return $token->isGivenKind(T_ENCAPSED_AND_WHITESPACE)
            || $token->isGivenKind(T_START_HEREDOC)
            || '"' === $token->getContent()
            || 'b"' === strtolower($token->getContent())
        ;
    }
Check if token is a part of a string.

@param Token $token The token to check

@return bool