Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
This does not appear to have been part of any formal specification. It was mentioned in HTML+ Discussion Document - Dave Raggett, November 8, 1993 (Section 5.9 - Images), but was not part of the first revision of HyperText Markup Language Specification - 2.0 in 1994.
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