Except for captions and images of text, text can be resized without assistive technology up to 200 percent without loss of content or functionality. (Level AA).
This success criterion requires that the text – both static and that are part of user interface components that are visible to the users must be resizable (scalable) to 200% without the help of any assistive technologies like screen magnifiers. Even though the user agents like the browsers that meet UAG (User Agent Guidelines) 1.0 bear the responsibility of scaling or zooming the text up to 200%, it is the authors responsible for providing that support to the browsers.
What do I do as the content author?
The authors or developers have to ensure:
Users with low vision or limited vision who consume the content without any assistive technology but use browsers’ zoom functionality alone.