Contains the regular expression to use when matching elements of the extended community list for a route. 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 ext_comm_exp_len of zero indicates that the field is not in use. This field is only relevant if bgpExtCommListEntryType is 'regular-expression'. It is otherwise ignored.