WCAG 2.1: Understanding Success Criterion (SC) 1.1.1 (Level A)
All non-text content that is presented to the user has a text alternative that serves the equivalent purpose...
Situation B: If a short description can not serve the same purpose and present the same information as the non-text content (e.g., a chart or diagram):...
WCAG 2.1: Sufficient Technique G74
G74: Providing a long description in text near the non-text content, with a reference to the location of the long description in the short description
Also consider:
WCAG 2.1: Understanding SC 1.3.1: Info and Relationships (Level A)
The intent of this Success Criterion is to ensure that information and relationships that are implied by visual or auditory formatting are preserved when the presentation format changes. For example, the presentation format changes when the content is read by a screen reader or when a user style sheet is substituted for the style sheet provided by the author.
Situation A: The technology provides semantic structure to make information and relationships conveyed through presentation programmatically determinable:
WCAG 2.1: Sufficient Technique G115: Using semantic elements to mark up structure
MathML, a markup language designed to maintain important distinctions between structure and presentation in mathematics, includes special "presentation" markup for the complex notations used to represent mathematical ideas as well as "content" (semantic) markup for the mathematical ideas themselves.
MathType full demo, with copyable text that pastes as full MathML