Alternative text (alt text) is text that describes the content of an image that can be read by a screen reader. It's important to consider what elements of the image are important to include in context. A portrait photo of a historical figure may just need that figure's name as the alt text, while a piece of art may need its primary features denoted, and a diagram or graph may need its contents fully described.
The Web Content Accessibility Guidelines version 2.0 require four pieces for a video to be considered accessible. In brief, those guidelines are:
The Order Panel is a more visual way to edit the tags in a PDF. It's more intuitive to use than the Tags Panel, but has some limitations. Thus, it should be the first step in checking a document after checking the accessibility and/or tagging it with Make Accessible.
The most straightforward process of correcting tags with the Order Panel is to go through the document twice. The first time, you will check the accuracy of the tags present, and in the second, you will check the reading order.
There are two approaches to creating captions and transcripts in YouTube, captions first and transcript first. Captions first will be the most common process in most cases, but if you're working from a script or you prefer to work in a text editor, you can skip to the Working From a Transcript section.
PDF is a curious case for accessibility. On one hand, it has the potential to be a useful standard for both accessible reading and for printing. On the other, it is rarely utilized in an accessible manner and has many obscure issues and odd behaviors that can lead to problems.
This page is concerned with tag structures. More information on working with tags can be found on the Using the Tags Panel page.
The Tags Panel displays the primary structure of the document. While the Order Panel provides tools to restructure what content is grouped together, how it is labeled, and when it is read, the Tags Panel gives more granular control over the latter two aspects. The order of the tags is the reading order of the document, moreso than that displayed by the Order Panel, and each tag serves a specific semantic purpose (besides grouping tags like <Part> and <Sect>).
Assistive technology (AT) is an umbrella term that refers to devices or software that provide aid to those with disabilities. In regards to digital accessibility, this includes screen readers, magnifiers, braille displays, speech recognition software, and alternative input devices, among others. This page collects some informational resources on AT and links to some useful tools.