There are instances when domains can be selected during face construction in a manner in which there is more than one physically separate location at which the last selected domain can be linked to the face as currently defined. In those cases, you must choose the linkage which is appropriate for your topology. When this occurs, the Domain-Face Linkages frame (show in the figure below) appears in the Assemble Block panel providing a list of possible linkages and two associated commands. Use Selected Link instructs Fidelity Pointwise to use the link currently selected in the linkages list and also highlighted in the Display window. Do Not Add Domain will remove the last selected domain from the current face definition.
In many cases, all of the linkage choices will be valid, as in the example shown in the figure below where the selected domains form a loop around a single, as yet unselected, domain. In this case both linkage choices are valid.
However, there can be topologies which require a specific linkage to be chosen for an appropriate block computational topology. The example in the figure below shows a topology where a structured block is desired, and the two selected domains form a single face. Only the highlighted linkage shown in the figure is valid in this particular case.