The MDEX Engine supports two internal spelling modules, either or both of which can be used by an application:

Generally, applications that only need to correct normal English words can enable just the default Aspell module. Applications that need to correct international words, or other non-English/non-word terms (such as part numbers) should enable the Espell module.

In certain cases (such as an English-language application that also needs to correct part numbers), both Aspell and Espell can be enabled.