How does the PHPCI framework distinguish between mobile phone and computer access?

How does the PHPCI framework distinguish between mobile phone and computer access to the php framework?

For example:
The a. php page is displayed directly when the computer accesses it.
The B. php page is displayed when the mobile phone is accessed.

Reply to discussion (solution)

$ _ SERVER ['http _ USER_AGENT ']

Function Reference
$ This-> load-> library ('User _ agent ');
If ($ this-> agent-> is_mobile ())
{
$ This-> load-> view ('A. php', $ this-> getpagedata ());
}
Else
{
$ This-> load-> view ('B. php', $ this-> getpagedata ());
}

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Is the CI framework such a debugging diagram? Need to add. php?