Update 2-ttcn-3_limitations_in_this_version.adoc

with { optional "implicit omit" }  limitations updated

usrguide/referenceguide/2-ttcn-3_limitations_in_this_version.adoc

@@ -50,6 +50,9 @@ function f_check() return boolean {
 * For record of/set of types of fixed size, which have a length restriction of one concrete value, and arrays the `sizeof()` and `lengthof()` predefined functions are not standard compliant: `sizeof()` returns the number of elements, `lengthof()` returns the index of the last initialized element plus one.
 * IPv6 networking between the MC, HC and Parallel Test Components is supported only on Linux and Cygwin 1.7.
 * The `optional "implicit omit"` attribute is not applied recursively.
+* The `optional "implicit omit"` attribute can be applied directly to global value and template definitions, but not to local value and template definitions.
+* The `optional "implicit omit"` attribute can be applied to a module, in which case it will have effect on global value and template definitions in the module,
+and local value and template definitions in the module, with the exception of (local) variable definitions
 * Templates using the `decmatch` (decoded content match, B.1.2.9 in <<13-references.adoc#_1, [1]>>) matching mechanism cannot be sent through test ports (doing so will result in a dynamic test case error). Template module parameters using `decmatch` are also not supported.
 * Since TITAN version R5B the matching symbol "*" (AnyValueOrNone, B.1.2.4 in <<13-references.adoc#_1, [1]>>) causes a compile time error when assigned to a mandatory field of a record or set template, as it is stated in the standard. This breaks backwards compatibility because in the older versions of TITAN only a warning was emitted.
 * When assigning a value to a structure using the value list notation, assignment notation or index notation (but not when assigning values to fields or elements one at a time), if the structure’s old value (or part of it) is referenced on the right hand side, the structure’s new value will only contain the fields or elements set in that assignment. All other fields or elements that may have been initialized in prior assignments will be set to unbound.