Track Hubs can now have hubs that filter on the additional fields. For example, if you have a standard BED file with the name field, you can now add a setting like the below to your track hub stanza to allow users to filter on that name:
By adding the setting "nameFilterText *" the UCSC Genome Browser expects to find a field with "name" in the bigBed that is attached for that track, where * is interpreted to display all named items by default with a wildcard match. A user can then click into the Track Settings and enter a more specific restriction. For example, if the bigBed for the Track Hub was a track of Transcription Factor Binding Sites (TFBS), by adding "nameFilterText *" a user would then have an option to go to the track and type JUN* in place of * and in the current view only named TFBS starting with JUN would display. Or a user could enter *UN* to select a wider set of TFBS items in the current view that included JUN items and other items with UN in the name. The option to use regular expressions is also provided beyond wildcards.
This new filtering setting can apply to any field that has text. If you had an additional field named "source" in the .as file used to create the bigBed, you should be able to add "sourceFilterText *" and then a filter on the source text information should work.
For numerical fields, there is also the ability to filter on numbers. For example, if you had a field numberOfEvents as defined in the -as file used to create the bigBed, you could have a setting line such as "numberOfEventsFilterValues 0" to say you wanted to allow a user to filter on these numerical values. By using 0 you are making all items visible, where raising the value would filter out some items by default upon first viewing the data.