HTML Checking for Large Sites

The <script> tag allows authors to include dynamic scripts and data blocks in their documents. When the src is present, this tag accepts a type attribute which must be either:

• an empty string
• text/javascript (that’s the default, so it can be omitted)
• module

Examples:

<!-- This is valid, without a type it defaults to JavaScript -->
<script src="app.js"></script>

<!-- This is valid, but will warn that it can be omitted -->
<script type="text/javascript" src="app.js"></script>

<!-- An empty attribute is valid, but will warn that it can be omitted -->
<script type="" src="app.js"></script>

<!-- The module keyword is also valid as a type -->
<script type="module" src="app.js"></script>

<!-- Any other type is invalid -->
<script type="wrong" src="app.js"></script>
<script type="text/html" src="app.js"></script>
<script type="image/jpeg" src="app.js"></script>

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 src attribute is a required attribute, so it cannot be blank.

Example:

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

The src attribute on an <img> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.

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" />

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>

This error message indicates that there is a backslash (\) used in a URL, which is not a valid character for URL paths.

You’ll need to replace the backslashes with forward slashes (/) in the URL path segments.

Here’s an example of a correct img tag using a valid URL path:

<img src="https://example.com/img/small/photo.png" alt="example image">

Also, make sure that the URL is correct and that the image file actually exists in the specified location.

The src attribute on an element <img> contains a character which is not allowed unless properly encoded.

Special characters needing encoding are: :, /, ?, #, [, ], @, !, $, &, ', (, ), *, +, ,, ;, =, as well as % itself.

For example, this image tag is incorrect because the src attribute contains an the unallowed characters [ and ]:

<img src="image[00].svg" alt="logo">

Instead, this is the properly percent-encoded src attribute, where [ has been replaced with %5B and ] with %5D.

<img src="image%5B00%5D.svg" alt="logo">

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 element <img> contains a character that is not allowed, and should be encoded.

Some typical examples include the pipe character | that should be replaced by its encoded alternative %7C , and the left square bracket [ that needs to be encoded as %5B.

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