This document discusses various PHP functions categorized into different groups like:
- Date Functions: date, getdate, setdate, Checkdate, time, mktime
- String Functions: strtolower, strtoupper, strlen, trim, substr, strcmp etc.
- Math Functions: abs, ceil, floor, round, pow, sqrt, rand
- User Defined Functions: functions with arguments, default arguments, returning values
- File Handling Functions: fopen, fread, fwrite, fclose to handle files
- Miscellaneous Functions: define, constant, include, require, header to define constants, include files etc.