The MSSelection module can be thought of as a compiler which compiles expressions written in MSSelection syntax into TaQL code. The module therefore can also be supplied pure-TaQL expressions which are used as-is along with any of the MSSelection expressions. Internally, the pure-TaQL expression will be treated as just another MSSelection expression.
While it is natual to be able to use TaQL expressions via the MSSelection module for selection on an MS, it is also possible to embed MSSelection expressions in TaQL expressions via the MSCal user-defined functions (UDF). E.g. in a TaQL expression like the following
sel1 and sel2 can be MSSelection baseline (section 3). Other types of selection are also similarly possible (e.g. selection on Time, Frequency, Scan, etc.) via TaQL.