Modernizr is an an excellent library used for client-side feature detection.
The full set of features detected can be obtained using its development version, however, including this entire file is not ideal in production - why make users download all the extra code for feature detection tests that will not ever be used?
Thankfully, Modernizr has a nifty download feature, which lets you fill in a form to select which tests you want, and then it generates a customised file for you to download.
That is great, however, what if you want to use Modernizr to generate custom files on the command line?
I came across this closed ticket raised against Modernizr, and that helped somewhat, as I found a way to generate custom files on the command line, but the command I had to issue was extremely convoluted.