Actually it is adding more than a /
If Joomla is installed in a subdirectory it includes (eg test-cms) that as well (eg (/test-cms/#to-some-position-on-page

https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/form/fields/url.php#L57

  // Note that the input type "url" is suitable only for external URLs, so if internal URLs are allowed
    // we have to use the input type "text" instead.

So I assume that this needs to be changed. https://github.com/joomla/joomla-cms/blob/staging/administrator/components/com_content/models/forms/article.xml#L674

Hello all. I was playing around with this for a bit this morning and was able to successfully achieve the # anchor links concept. However, I don't think it is the best solution because I could not figure out how/where to update the URL Validation portion to accept #my-anchor-link as a valid entry into the Link fields on the edit Article view.

Steps I Took

1.) Added the following code to the form.php file. Code was added in starting at line 1382: https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/form/form.php#L1382

// If it starts with a "#" assume an anchor link.
elseif (substr($value, 0, 1) == '#')
{
  return $value;
}

2.) Please keep in mind this is the part I don't like... I removed validate="url" from the article.xml file at lines 678, 710, and 742.

Ideally there is an adjustment we can make to the URL Validation file to allow # to lead off what people enter into the fields, but I could not figure it out. I tried to add '#' to the $scheme = array() seen on the URL Rule File https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/form/rule/url.php#L54

Hopefully someone with better knowledge of the URL Validation can add some input here :)

See: #8125