If not representing one or more ORF entries this contains the regular expression to use when matching elements of the extended community list for a route. If representing ORF entries then instead of a regular expression this contains a simple comma separated list of extended communities which are or-ed together when matching. In both cases this is stored here in ASCII format. Extended communities are matched as hexadecimal numbers. For example, the extended community '0x112233445566ab' should be represented in the string as '00112233445566AB' (leading zeroes are necessary to make the length up to 8 bytes). Alphabetic nibbles 'A' through 'F' must be specified in upper case. The string is not NULL-terminated. A NULL string or a match_ext_comm_exp_len value of zero indicates that the field is not in use.