Guideline 4:
Provide ways of checking and correcting inaccessible content.

Many authoring tools allow authors to create documents with little or no knowledge about the underlying markup. To ensure accessibility, authoring tools must be designed so that they can (where possible, automatically) identify inaccessible markup, and enable its correction even when the markup itself is hidden from the author.

Authoring tool support for the creation of accessible Web content should account for different authoring styles. Authors who can configure the tool's accessibility features to support their regular work patterns are more likely to accept accessible authoring practices (refer to guideline 5). For example, some authors may prefer to be alerted to accessibility problems when they occur, whereas others may prefer to perform a check at the end of an editing session. This is analogous to programming environments that allow users to decide whether to check for correct code during editing or at compilation.