How exactly does PHP get the form data

When the form is submitted to the browser after the initial processing, upload to the php form processing page.
The average book is either to automatically assign variables to form elements, or to save the submitted data in a global array, and then call the system-specific array of automatic global variables to get the values. Read for a long time did not understand how PHP and the browser to communicate information, that is, B (client) to send data, to S (server) of the php form processing page, and then produce the corresponding variables, the middle of PHP working mechanism, which boss clear Ah! Has not understood!

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