Description: The bit mask which, in combination with the corresponding instance of viewSubtree, defines a family of view subtrees. Each bit of this bit mask corresponds to a sub- identifier of viewSubtree, with the most significant bit of the i-th octet of this octet string value (extended if necessary, see below) corresponding to the (8*i - 7)-th sub-identifier, and the least significant bit of the i-th octet of this octet string corresponding to the (8*i)-th sub-identifier, where i is in the range 1 through 16.

Each bit of this bit mask specifies whether or not the corresponding sub-identifiers must match when determining if an Object Identifier is in this family of view subtrees; a '1' indicates that an exact match must occur; a '0' indicates 'wild card', i.e., any sub-identifier value matches.

Thus, the Object Identifier X of an object instance is contained in a family of view subtrees if the following criteria are met:

for each sub-identifier of the value of viewSubtree, either:

the i-th bit of viewMask is 0, or

the i-th sub-identifier of X is equal to the i-th sub-identifier of the value of viewSubtree.

If the value of this bit mask is M bits long and there are more than M sub-identifiers in the corresponding instance of viewSubtree, then the bit mask is extended with 1's to be the required length.

Note that when the value of this object is the zero-length string, this extension rule results in a mask of all-1's being used (i.e., no 'wild card'), and the family of view subtrees is the one view subtree uniquely identified by the corresponding instance of viewSubtree.