   #PHP Manual Output Control Functions ob_implicit_flush Object property
   and method call overloading

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                                   ob_start

   (PHP 4 )
   ob_start -- Turn on output buffering

Description

   bool ob_start ( [callback output_callback])

   This function will turn output buffering on. While output buffering is
   active no output is sent from the script (other than headers), instead
   the output is stored in an internal buffer.

   The contents of this internal buffer may be copied into a string
   variable using ob_get_contents(). To output what is stored in the
   internal buffer, use ob_end_flush(). Alternatively, ob_end_clean()
   will silently discard the buffer contents.

   An optional output_callback function may be specified. This function
   takes a string as a parameter and should return a string. The function
   will be called when ob_end_flush() is called, or when the output
   buffer is flushed to the browser at the end of the request. When
   output_callback is called, it will receive the contents of the output
   buffer as its parameter and is expected to return a new output buffer
   as a result, which will be sent to the browser. If the output_callback
   is not a callable function, this function will return FALSE.

     Note: In PHP 4.0.4, ob_gzhandler() was introduced to facilitate
     sending gz-encoded data to web browsers that support compressed web
     pages. ob_gzhandler() determines what type of content encoding the
     browser will accept and will return it's output accordingly.

     Note: Before PHP 4.3.2 this function did not return FALSE in case
     the passed output_callback can not be executed.

   Output buffers are stackable, that is, you may call ob_start() while
   another ob_start() is active. Just make sure that you call
   ob_end_flush() the appropriate number of times. If multiple output
   callback functions are active, output is being filtered sequentially
   through each of them in nesting order.

   ob_end_clean(), ob_end_flush(), ob_clean(), ob_flush() and ob_start()
   may not be called from a callback function. If you call them from
   callback function, the behavior is undefined. If you would like to
   delete the contents of a buffer, return "" (a null string) from
   callback function.

   Example 1. User defined callback function example
   <?php
   function callback($buffer) {
     // replace all the apples with oranges
     return (str_replace("apples", "oranges", $buffer));
   }
   ob_start("callback");
   ?>
   <html>
   <body>
   <p>It's like comparing apples to oranges.
   </body>
   </html>
   <?php
   ob_end_flush();
   ?>

   Would produce:
<html>
<body>
<p>It's like comparing oranges to oranges.
</body>
</html>

   See also ob_get_contents(), ob_end_flush(), ob_end_clean(),
   ob_implicit_flush() and ob_gzhandler().
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