Microsoft Indexing Service uses filters, much like application extensions, to interpret given file types into easily searchable text. FileLocator Pro can use these indexing service filters, without the need to run the indexing service, to help convert files into easily searchable text.
The list of currently installed IFilters is shown in the IFilter settings tab. To use the IFilter activate it via the Enhanced File Search settings in the Options tab
A list of free IFilters can be found using a simple Internet search.
By default IFilters for HTML/XML based file types are not used because many users want to be able to search the tags within an HTML document not just the text. However, if you want to search just the text of HTML/XML files you can include the IFilters by checking the Include IFilters for HTML/XML based file types.
The IFilter Search Priority determines which type of extension should be used for processing a file if both an IFilter AND an application specific processing extension are registered. By default IFilters are Secondary, ie they will only be used if an application specific extension is not found or could not load the given file.