With Super Speedy Filters you can enable ‘multiselect’ for taxonomies or attributes.
With multiselect, you can choose to narrow or expand the results. If your multiselect is not working, please check these potential causes and their solutions.
Ignore Filters is selected
Check if you have ‘Ignore other filters’ enabled in the widget – if so, this will cause the widget to reset the URL and clear all other taxonomies and attributes which also affects multiselect. In order for multiselect to work, you need to have ‘Respect other filters’ selected.
Multiselect on hierarchical taxonomies
Multiselect may misbehave if you use it on a hierarchical taxonomy – e.g. if you allow users to select items at different levels (display hierarchy rather than display top or children) – this is because /clothing/t-shirts/ gets resolved to the t-shirts term-id, but /clothing/t-shirts/watches/ would not make sense. Avoid using hierarchical display if you wish to use multiselect on your hierarchical taxonomies.
You can still use multiselect with hierarchical taxonomies, but it should be on ‘children’ or ‘top level’ display options to avoid hierarchical conflicts.