If not representing one or more ORF entries this contains the regular expression to use when matching elements of the community list for a route. If representing ORF entries then instead of a regular expression this contains a simple comma separated list of communities which are or-ed together when matching. In both cases 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 ma_comm_exp_len of zero indicates that the field is not in use.