This section is an overview of concepts and conventions used throughout the IESDP and serves as a continuation of the Infinity Engine File Format Hacking Project.

All versions of the Infinity Engine, except that used in Planescape: Torment, make some internal of the Lua programming language, as developed by TeCGraf at the Pontifical Catholic University of Rio de Janeiro in Brazil. In the Infinity Engine, LUA is primarily used for the cheats/debugging console. The debug console actually allows complete LUA programs to be entered and run, though these programs can only have a very limited affect on the game and the engine. The LUA documentation is available online, though knowledge of LUA is of limited use in IE modding. It should be mentionned, that unlike other engines where LUA is used, the Infinity Engine AI scripts have nothing to do with LUA.

The data types used to describe the file formats used by the Infinity Engine are:

Data type	Description
char array	An array of ASCII characters of a fixed length
ASCIIZ string	An array of ASCII characters terminated by a NUL character (ASCII 00). Note that the full length of the array need not be used, and may in fact contain garbage data, so long as a NUL character is found earlier in the array to mark the end of valid data.
word	A little-endian "word" of 16-bits
dword	A little-endian "double-word" of 32-bits
point	A point within some reference frame, composed of two 16-bit words; the first is the x-coordinate and the second is the y-coordinate.
rect	A rectangle within some reference frame, composed of 4 16-bit words; the order of the coordinates is: left, top, right, bottom. Typically this is used to store bounding boxes of various objects.
strref	A reference into the 'TLK' resource. Stored as a 32-bit number (though the top 8 bits refer to an internal file Id, e.g. 0x01 refers to dialogf.tlk) which can be mapped to a string via a lookup into the TLK table.
resref	A reference to a specific resource -- a string (max 8 characters) which is mapped to a resource (stored in a BIF file or an override directory) via the KEY file. Note that these are always treated as 8 characters long; unused characters should generally be filled with NUL bytes.

Several file types are used in the Infinity Engine. These file types can be identified in three different ways. First, most file formats have a numerical code (e.g. 0x03e8), called the resType. Second, all file formats have a file extension (e.g. 2da), which is used to determine what format the data inside is expected to be. Third, most of the file formats contain a 4-byte signature string in the file header to indicate the file type, and a 4-byte version string to indicate the file format version.