INFLD looks for INFLD.DEF in system or user memory at runtime. If found, it reads the first line of characters from the file and interprets them as additional type codes. This is a handy way of experimenting with many of the miscellaneous and timer-related type codes which you could safely add to any category of field.
To create the INFLD.DEF file, just use VUE or another editor to create an ordinary text file whose top line is a string of valid type characters. Save the file to disk and use the LOAD or SYSTEM commands to load it into user or system memory.
Searching for the INFLD.DEF file adds another few jiffies of execution time to INFLD. You can reduce this by loading INFLD.DEF into memory immediately after the INFLD. INFLD checks there first before doing a general search. If you are not using the INFLD.DEF facility, you can disable the search for it in memory by using the m type code.