ECC 200 allows flexible encodation of data. If the capacity of a single symbology cannot encode a long message, a Structured Append sequence of up to 16 separate but logically linked ECC 200 symbols may be employed to encode it.

Codeword 233 is always encoded in the first symbol character position to denote that the symbol is part of a Structured Append. Behind it, three Structured Append codewords immediately follow. The first codeword is the symbol sequence indicator which shows the position of the symbol within the set
(up to 16) of ECC 200 symbols. It is made up of eight bits. The first four bits denote the position of the particular symbol while the last four bits denote the total number of the symbols.

The symbol sequence indicator is closely followed by two codewords treated as file identification. These two codewords aims to increase the probability that only logically linked symbols are processed as part of the same message. The file identification is defined by the value of its two codewords, each of which may have a value 1 to 254. This feature leads to the 6, 4516 different file identifications.

In order to encode data to meet specific industry standards as authorized by AIM Inc., FNC 1 should occur in ECC 200. In Structured Append form, two codewords for FNC 1 usage shall be placed in the fifth and sixth codeword positions just after the first four codewords used for Structured Append. In the second and subsequent symbols, FNC 1 shall not occur in these positions, except when used as a field separator.

The Extended Channel Interpretation (ECI) is used to identify a particular code page or more specific data interpretation. The ECI protocol, fully specified in AIM Inc. International Technical Specification - Extended Channel Interpretations Part 1, allows the output data stream to have interpretations different from that of the default character set and provides a consistent method to specify particular interpretations on byte values before printing and after decoding.

In Data matrix, the ECI is identified by a 6-digit number encoded in the Data Matrix symbol by the ECI character. It should be noted that the ECI can only be used with readers being able to transmit the symbology identifiers. There is an exception that if the ECI(s) can be handled entirely in the reader, the ECI can also be used.

The ECI protocol only applies to ECC 200 in Data Matrix and supports the following four broad types of interpretations in this barcode: