Why this is needed
This will allow for the following:
1. Allow users to filter by text fields instead of just select fields that are enabled in layered navigation. This would enable a narrow down feature in the category. Whether they searched by name, manufacturer, author etc. Imagine a book store listing 100,000 authors in layered navigation… Not possible, but with this feature they could search by author and other fields easily!
2. Allow users to search in select fields that are simply too large to display in layered navigation. An example of such would be printer cartridges. The list of different printer models is simply too great (in the 100s) to display in layered navigation or categories. However, in order to find the right cartridge the user will need to search in something.... And searching the “printer model” attribute makes the most sense.
In the frontend navigation have a search box with a pull down box of attributes and a text field the user can enter in a search value. Once searched the user can remove the “search filter” or add another “search filter”
For each attribute add a flag that says searchable attribute in navigation. The reason for this is because more attributes can be searched than can be in layered navigation (for example, text fields) and some attributes you may not want to be searched but may be in layered navigation. Then add the search widget as described above