The alt attribute is intended for short text alternatives. If a short description can not present the same information as the content (e.g., a chart or diagram), it must be combined it with a long description. The long description may be provided by an aria-describedby attribute, which references to a different element containing text describing the content. Another possibility is to provide the long description as part of the standard presentation (i.e., everyone receives it). The description is located near the non-text content but does not have to be the very next item. For example, there may be a caption under a chart with the long description provided in the following paragraph. The location of this long description is then provided within the short text alternative so the user knows where to look for it if they cannot view the non-text content. E.g.: “October sales chart . Details in text following the chart”.
Engine scans for alt attributes with over 250 characters
Users who use assistive tools, such as screen readers will fail to understand properly the content of the image
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