Two or more may be combined to form a new by joining them with the "+" symbol. This is particularly useful where both concepts are primitive. The resultant is the of each of the in the . The resultant below represents a drug dose form that is both a spray and a suspension.
421720008|Spray dose form| + 7946007|Drug suspension|
Although not stipulated by the syntax, the two joined in this way must (in nearly every case) come from the same top level . A rare exception to this rule is those expressions which refer to products that are both drugs and devices, and are therefore descendants of both 373873005 |pharmaceutical / biologic product| and 260787004 |physical object|.
The syntax does not mandate which in the should have associated terms and which should not, so it is valid (although not advisable) to mix and match. For example, the following syntax is valid: The syntax allows spaces, tabs and carriage returns in most places. The following example has an identical meaning to the one above: