SYSML17 — How to interpret non-Navigation

An “X” on a single end of an association to indicate that an end is not navigable has similarly been dropped

Does this statement mean that SysML has no concept of non-Navigation (only unspecified)... or does it mean that if you
have an association end A has no Navigation shown, end B has Navigation shown... then End A should be interpreted as
being non-Navigatable...

The standard would indicate this as it says "has been similarly dropped" which means it is not shown but it is there all the same...