Filter the string to include only the allowed characters
Permits all characters listed in allowed-chars, filtering all others outs. In addition to literally listing the characters, you may also use ranges of characters (delimited by a
Hexadecimal characters started with a
Octal characters started with a
\0 (i.e. \040)
\r are recognized.
This documentation was imported from Asterisk Version SVN-branch-13-r420538