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.
Note that the majority of form control labels are text-based. Using images as labels meets the requirements of the criterion, but care should be taken to ensure that the images are widely understood by the intended target audience. Authors may consider providing additional hints, such as text-based tooltips or supplementary text, to support clarity when using image-based labels.
This success criterion does not require that labels or instructions be correctly marked up, identified, or associated with their respective controls — that 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 — that aspect is
covered separately by 4.1.2 Name, Role, 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 accurate, sufficiently clear, or descriptive is covered separately by 2.4.6 Headings and Labels.
The use of "requires" in this criterion's normative wording does not mean that the criterion only applies to required form fields. It is used here as a synonym for "accepts", "expects", or "allows". The criterion applies to all form fields, whether they're required or optional.