Group codes and the associated values define a specific aspect of an object or entity. The line immediately following the group code is the associated value. This value can be a string, an integer, or a floating-point value, such as the X coordinate of a point. The lines following the second line of the group, if any, are determined by the group definition and the data associated with the group.
Special group codes are used as file separators, such as markers for the beginning and end of sections, tables, and the end of the file itself.
Entities, objects, classes, tables and table entries, and file separators are introduced with a 0 group code that is followed by a name describing the group.
The maximum DXF file string length is 256 characters. If your AutoCAD drawing contains strings that exceed this number, those strings are truncated during SAVE, SAVEAS, and WBLOCK. OPEN and INSERT fail if your DXF file contains strings that exceed this number.