This is the (unofficial) Intel x86 and IA-32 instruction docset for Dash / Dasht / Zeal.
Since there seems to be no official HTML documentation by Intel, this uses the unofficial HTML version generated from the Intel's Developer Manual PDFs (Volume A and Volume B) by Félix Cloutier's x86doc script.
The HTML docs are also available online.
You can use the gen-docset.sh script to (re-)generate the docset.
It's possible to add the docset to your reader via this feed:
https://homepage.ruhr-uni-bochum.de/jan.holthuis/downloads/Intel_x86_IA32.xml