The trinocular operation is compiled into an if statement. What to do with it

The trinocular operation is compiled into an if statement ...
And the red one, what's the concept?

$KEYC = $ckey _length? ($operation = = ' DECODE '? substr ($string, 0, $ckey _length): substr (MD5 (Microtime ()),-$ckey _length)): ";



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The 2nd parameter of the SUBSTR function is turned over the manual. Where to start the interception
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And the red one, what's the concept?

$KEYC = $ckey _length? ($operation = = ' DECODE '? substr ($string, 0, $ckey _length): substr (MD5 (Microtime ()),-$ckey _length)): ";

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PHP Code

if ($ckey _length) {    if ($operation = = ' DECODE ') {        $keyc =substr ($string, 0, $ckey _length);    } else{        $KEYC =substr (MD5 (Microtime ()),-$ckey _length);}    } else{    
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