I am very aware that it is trivial to handle notices, errors and warnings. The problem is that PHP does not do this by default which allows people to exploit undocumented behavior.

As for handling invalid input, I think you should actually check what some of the functions output some day.

For example, decbin clearly states that the input should be an integer but if I pass it a string.....

Code/ctsr » php -r 'echo decbin("invalid input");' 0%

Zero is clearly not a NULL value. This is one I ran into this morning with php 5.3.8, I've seen this issue crop up in many other functions, they don't return NULL. Some return NULL, some return 0, some return '', some return '0', some return FALSE.