The intent of this Success Criterion is to have content authors present instructions or labels that identify the controls in a form so that users know what input data is expected. In the case of radio buttons, checkboxes, comboboxes, or similar controls that provide users with options, each option must have an appropriate label so that users know what they are actually selecting. Instructions or labels may also specify data formats for data entry fields, especially if they are out of the customary formats or if there are specific rules for correct input. Content authors may also choose to make such instructions available to users only when the individual control has focus especially when instructions are long and verbose.
The intent of this Success Criterion is not to clutter the page with unnecessary information but to provide important cues and instructions that will benefit people with disabilities. Too much information or instruction can be just as harmful as too little. The goal is to make certain that enough information is provided for the user to accomplish the task without undue confusion or navigation.
This Success Criterion does not require that labels or instructions be correctly marked up, identified, or associated with their respective controls - this aspect is covered separately by 1.3.1: Info and Relationships. It is possible for content to pass this Success Criterion (providing relevant labels and instructions) while failing Success Criterion 1.3.1 (if the labels or instructions aren't correctly marked up, identified, or associated).
Further, this Success Criterion does not take into consideration whether or not alternative methods of
providing an accessible name or description for form controls and inputs has been used - this aspect is
covered separately by 4.1.2: Name, Role and Value. It is possible
for controls and inputs to have an appropriate accessible name or description (e.g. using aria-label="...")
and therefore pass Success Criterion 4.1.2, but to still fail this Success Criterion (if the labels or instructions
aren't presented to all users, not just those using assistive technologies).
This Success Criterion does not apply to links or other controls (such as an expand/collapse widget, or similar interactive components) that are not associated with data entry.
While this Success Criterion requires that controls and inputs have labels or instructions, whether or not labels (if used) are sufficiently clear or descriptive is covered separately by 2.4.6: Headings and Labels.
Providing descriptive labels AND one of the following:
The techniques at the end of the above list should be considered "last resort" and only used when the other techniques cannot be applied to the page. The earlier techniques are preferred because they increase accessibility to a wider user group.