Contains the regular expression to use when matching elements of the community list for a route. This is stored here in ASCII format. Communities are matched using new-format decimal notation. For example, the community '0x00120101' should be represented in the string as '18:257'. The string is not NULL-terminated. A NULL string or a comm_exp_len of zero indicates that the field is not in use. This field is only relevant if bgpCommunityListEntryType is 'regular-expression'. It is otherwise ignored.