CategoryURL - JBrowse plugin

Add URL parameter "cat" to specify a category of tracks to display.
All tracks with the given category will be displayed.
If any "tracks" are specified in the URL, "cat" tracks will be appended to list.

Usage: Add &cat=myCategory
Result: all tracts with category "myCategory" will be displayed.
Sub-categories are supported as well (i.e. "&cat=myCategory/mySubCategory"

The cat= URL parameter allows the display of tracks with the given category 
defined in the track metadata that are used to group tracks in the hierarchical 
track selector.  For example:

"category" : "Miscellaneous",

Example:
http://<jbrowse>/?data=sample_data/json/volvox&cat=Miscellaneous
http://<jbrowse>/?data=sample_data/json/volvox&cat=Quantitative/Density

Install / Activate:

For JBrowse 1.11.6+, copy the CategoryUrl directory to the JBrowse 'plugins' directory.
Add this to appropriate trackList.json under the plugins section (create section, if it doesn't exist):

   "plugins": [ 
        'CategoryUrl'
    ],

