Spelling correction is a closely-related feature to stemming and thesaurus functionality, because spelling auto-correction essentially provides an additional mechanism for computing alternate versions of the user query. In the MDEX Engine, spelling is handled as a higher-level feature than stemming and thesaurus. That is, spelling correction considers only the raw form of the user query when producing alternate query forms.

Alternate spell-corrected queries are then subject to all of the normal stemming and thesaurus processing. For example, if the user enters the query telvision and this query is spell-corrected to television, the results will also include results for the alternate forms televisions, tv, and tvs.

Note that in some cases, the Thesaurus feature is used as a replacement or in addition to the system's standard spelling correction features. In general, this technique is discouraged. The vast majority of actual misspelled user queries can be handled correctly by the Spelling Correction subsystem. But in some rare cases, the Spelling Correction feature cannot correct a particular misspelled query of interest; in these cases it is common to add a thesaurus entry to handle the correction. If at all possible, such entries should be avoided as they can lead to undesirable feature interactions.