The World Wide Web Consortium (W3C) publishes web standards for creating accessible web content. a11y Australia audits websites, apps and documents against these standards, but considers them a starting point for creating truly inclusive content.

We find these resources super useful, and hope you do to: 

Standard Description
Quick reference guide: Web Content Accessibility Guidelines WCAG) Called 'How to meet WCAG 2', this quick reference guide is really handy. Don't be bamboozled by complex explanations of WCAG principles, guidelines and success criteria... find it what it really means. Of course you can peruse the full specification document for WCAG 2 if you need to.
Authoring practices: Accessible Rich Internet Applications (ARIA) ARIA is a markup language that explains dynamic widgets, like show/hide accordion content, menus, dialog boxes, toggle buttons, tooltips and non-semantic scripted elements to users who are blind and using assistive technologies like screen readers and Braille devices. Developers and testers, make it your daily go-to guide to understand expected screen reader announcements and keyboard interactions. Again, here's the full ARIA specification
Other standards There are a range of other relevant web standards, including HTML itself, the language of the web, the User Agent Accessibility Guidelines (UAAG) and Authoring Tool Accessibility Guidelines. But just remember, we know them so you don't have to.