All characters that are defined in the C3D file format are limited to standard 7-bit ASCII values from decimal 32 to 126.  When characters are used in C3D parameter and group names, only upper case characters A-Z, the underscore “_” and 0-9 are permitted to conform to the C3D standard, and ensure universal compatibility for all software applications.

However, user entered data, stored in the LABELS and DESCRIPTIONS parameters or in application specific groups like SUBJECTS and EVENTS, may use alternate UTF-8 character sets, but be aware that applications that do not support UTF-8 encoding may display these incorrectly.  The use of UTF-8 encoding as specified by RFC3629 is permitted but, if ASCII parameters are edited and converted to UTF-8 encoding, then applications may need to extend the parameter array storage to handle the larger byte count.