frameborder

Frameborder is an HTML attribute historically used with frame-related elements to control whether a visible border surrounds an embedded document. In practice, it appears on elements such as iframe and frame, where the values are typically "0" (no border) or "1" (default bordered). The attribute originated in older HTML specifications to provide a simple way to style embedded content without CSS.

In modern practice, frameborder is deprecated in HTML5 and is not a standard attribute in current specifications. Browsers that follow HTML5 may ignore it, and the traditional frames and frameset elements themselves are also obsolete in favor of CSS-based layouts and the iframe element. When borders are needed or removed today, the recommended approach is to use CSS, for example with style="border:0" or CSS rules such as iframe { border: 0; }.

Compatibility notes: frameborder may still be recognized by some older or backward-compatible browsers, but relying on it is discouraged. For historical web pages, the attribute might have been used to achieve consistent border behavior across different browsers, but modern development should avoid it.

See also: iframe, frames, CSS borders, HTML5 deprecations. Examples: <iframe src="example.html" frameborder="0"></iframe> represents the legacy usage; in HTML5 this would be written with CSS to remove the border, such as <iframe src="example.html" style="border:0"></iframe>.