Requirement
ObjectARX, .NET and ObjectDBX modules
The maximum name length in the AcDbSymbolTableRecord and AcDbDictionary classes is controlled by the $EXTNAMES system and header variable. Applications should check and honor this value. The main purpose of $EXTNAMES is to guard against non-compliant applications by setting the value to 0.
Compliant applications allow $EXTNAMES to be set to 1, and do not assume limits on the length of symbol names. User interface display of symbol names may be limited as necessary, and you can facilitate the viewing and editing of names via scrolling, stretching the displayed field, or other UI techniques.
When $EXTNAMES is set to 0, applications should not allow the creation of symbol names longer than 31 characters, but should still recognize longer names, and leave them unchanged. Use the function acdbSNValid() to accomplish this; it will account for the $EXTNAMES when validating a name. DWG and DXF save and wblock operations will "mangle" longer names as appropriate when $EXTNAMES is 0.