See Funge-98 final specification for official one. This page tries to track its interpretations and clarifications.
What size exactly is left up to the implementer. It doesn’t prohibit arbitrary-precision integer. But as you can see, otherwise the spec is too vague for such case. PyFunge uses arbitrary-precision integer from Python.
There is no enforced convention for what any given Funge-98 source file name ends in […], but .b98 is a good choice for Befunge-98 sources - “standard” example programs use this suffix. The spec doesn’t give explicit suffix for Unefunge-98 and Trefunge-98 sources. Maybe
.t98? > PyFunge uses these prefixes.
The Funge-98 character set overlays the ASCII subset used by Befunge-93 and may have characters greater than 127 present in it (and greater than 255 on systems where characters are stored in multiple bytes; but no greater than 2,147,483,647.) The source encoding is not specified, and any program relys on it is not portable. But every supported encoding should be ASCII-compatible, so UTF-16 cannot be used. PyFunge treats every source code as ASCII, not ISO-8859-1 nor UTF-8.
Subsequent lines in Unefunge are simply appended to the first, and the end of the source file indicates the end of the (single) line. End-of-line markers are never copied into Funge-Space. In the other words, Unefunge code can be split into several lines and they are concatenated before loading.
In Trefunge-98, the Form Feed (12) character increments the z coordinate and resets the x and y coordinates to zero. It is expected that form feed in Befunge-98 should be treated as like newline in Unefunge-98, but it is unclear.
# “Trampoline” instruction moves the IP one position beyond the next Funge-Space cell in its path. It is unclear what is the next Funge-space cell exactly.
y) should skip a (imaginary) space outside or a cell at other boundary. PyFunge skips an imaginary space outside.
; is truly ethereal; like space, it cannot ever be truly executed, in the sense of it taking up a tick and doing something. This means, if one IP’s path contains only
;s, it will block while finding next instruction, not marker.