Esoteric HTML - ismap vs CSS
a day ago
- The HTML 'ismap' attribute on <img> elements sends click coordinates as query parameters to the server.
- Coordinates sent by 'ismap' are based on the image's layout size (CSS pixels), not its natural or declared size.
- CSS resizing, user stylesheets, or accessibility tools can distort these coordinates, breaking server-side logic that relies on them.
- This behavior is consistent across major browsers, making 'ismap' risky unless CSS is guaranteed not to alter the image size.
- The author advises against using 'ismap' due to the unpredictability of layout-based coordinates.
- Comments highlight nostalgic uses of image maps and note that '<input type="image">' has a similar coordinate-sending behavior.
- Some users report that the 'ismap' article broke RSS readers due to unencoded '<marquee>' in the content.