Description:
------------
---
From manual page: http://www.php.net/function.substr#refsect1-function.substr-
parameters
---

"""
If length is given and is positive, the string returned will contain at most 
length characters beginning from start (depending on the length of string).

If length is given and is negative, then that many characters will be omitted 
from the end of string (after the start position has been calculated when a 
start is negative). If start denotes the position of this truncation or beyond, 
false will be returned.

If length is given and is 0, FALSE or NULL an empty string will be returned.

If length is omitted, the substring starting from start until the end of the 
string will be returned.
"""

And what if one needs to specify a value for length and obtain the last 
behavior??

That is:

if (/*whatever*/) $length=/*something*/;
else if (/*whatever_else*/) $length=/*something else*/;
else if.....
//...

echo substr ($string, $start, $length);


I guess the solution is to set $length=PHP_INT_MAX.

But then it needs to be better documented by declaring it as the default value 
for $length:

  replace this:
    string substr ( string $string , int $start [, int $length ] )

  with this:

    string substr ( string $string , int $start, int $length=PHP_INT_MAX )


Default values for all parameters must ALWAYS be documented, so that one can 
ALWAYS know what value to pass to a function when one has to specify a value and 
one wants the default behavior.

I have found the same problem in various pages of php's docs.
Actually there are cases worst than this (in this case, one can guess it).