Can anyone explain this PHP code using json_encode and json_decode?

  $a = '{ "tag": "<b></b>" }';
  echo json_encode( json_decode($a) );

This outputs:

{"tag":"<b><\/b>"}

when you would think it would output exactly the input. For some reason json_encode adds an extra slash.

From stackoverflow

• Because it's part of the JSON standard

  http://json.org/

  char

  any-Unicode-character-
      except-"-or-\-or-
      control-character
  \"
  \\
  \/ <---- see here?
  \b
  \f
  \n
  \r
  \t
  \u four-hex-digits
  

  From Peter Bailey

• That's probably a security-feature. The escaped version (Eg. the output) would be parsed as similar to the unescaped-version, by Javascript (Eg. \/ becomes /). Having escaped the slash like that, there is a lesser chance of the browser misinterpreting the Javascript-string as HTML. Of course, if you treat the data correct, this shouldn't be needed, so it's more a safeguard against a clueless programmer messing things up for himself.

  From troelskn

• Your input is not valid JSON, but PHP's JSON parser (like most JSON parsers) will parse it anyway.

  John Millikin : What's invalid about it?
  From Scott Reynen