HTML Checking for Large Sites

The seamless attribute was proposed to be included in the HTML5 spec, but it wasn’t finally accepted, so it’s not a valid attribute for <iframe>.

The src attribute for <img> tags is required, to define the source of the image, like in this example:

<img src="photo.jpg" alt="wombat" />

The <iframe> element, used to embed another document inside the current document, accepts both attributes width and height which must be valid non-negative integers. Percentages are not allowed for these attributes.

Check https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-iframe-element.

An <iframe> element allows to embed an HTML document inside another HTML document, and its src attribute is indicated the source URL of the embedded web page. The query part of that URL contains one or more space characters, which are not allowed, for example:

<iframe src="https://maps.google.it/maps?q=2700 6th Avenue"></iframe>

You should properly escape all space characters as %20 like this:

<iframe src="https://maps.google.it/maps?q=2700%206th%20Avenue"></iframe>

Learn more:

• HTML Living Standard: src attribute on iframe

Space characters are not allowed in src attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:

<img src="https://example.com/?s=some term" alt="description" />

<img src="https://example.com/?s=some%20term" alt="description" />

The src attribute on an <img> tag is not allowed to contain space characters. You should replace them with “%20“.

The <iframe> element, used to embed another document inside the current document, accepts both attributes width and height which must be valid non-negative integers. Percentages are not allowed for these attributes.

Check https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-iframe-element.

<img> tags used to display images require the attribute src to indicate the source of the image, for example <img src="/img/photo.jpg" />.

<iframe> tags are used to embed another document within the current document. To indicate the contents of that nested document, you can either use the src attribute with an URL, or directly provide the contents with the srcdoc attribute. Examples:

<!-- This will embed a document by its URL -->

<iframe src="https://example.com"></iframe>

<!-- This will embed the contents provided in the srcdoc attribute -->

<iframe srcdoc="<p>some content</p>"></iframe>

<!-- This is invalid -->

<iframe><p>some content</p></iframe>