The Nano-10, FMD and F-series PLCs only have 60K bytes of file space to store user's control web page.
These PLCs use a very simple file system. File name can only start with one character (0,1,2,....9,A,B,C....)and can have only 3 character extension.
Each file name is allotted 2K bytes of space but each file name can occupy multiple slots, in which case it takes over the space of other files.
That means 0.xxx will occupy the first 2K bytes, 1.xxx will occupy the next 2K bytes, and so on. A file may extend beyond its own allocated file space and take over the space of its adjacent files.
E.g. 0.xxx can occupy the space of 1.xxx and 2.xxx, therefore allowing you to store a file that is up to 6K bytes long. However, that also means you cannot store any file with name 1.xxx or 2.xxx or it will overwrite the data. Your next file should occupy file name from 3.xxx onwards.
The default control web pages 0.htm is > 2K bytes but < 4K bytes, and therefore occupy the space of 0.xxx and 1.xxx. The second control web page is therefore stored at 2.htm. If you need to store your own special files, such as small JPG or CSS file, they can be stored from 4.xxx up to before N.xxx.
More complex graphics or css file can be stored on any internet or intranet webserver (or stored in the TLServer's /public folder) instead of on the CPU flash memory.