PHP 4, PHP 5, PHP 7, PHP 8
ob_start - Turn on output buffering

Example #1 User defined callback function example

Result: <html> <body> <p>It's like comparing oranges to oranges.</p> </body> </html>
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Example #2 Creating an unerasable output buffer

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Example #3 of ob_start

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Function ob_start:

Output Buffering Control Functions

Most used PHP functions