The url field is a non-html text field to display the literal text version of a url. It lacks the ability to function as a source of data for an actual link and contains no link attributes, anchor text, or the ability to enclose text as an anchor with a [/url_field] wrapper. Please consider adding these.
In the absence of an html/flexible text field type or “link” field, if the shortcode for the current url field had attributes enabled, it could be used to wrap an element or existing text on a page in order to link the object being wrapped by the link/url shortcode and point the link to the url inside the custom field.
Here is some [url_field_shortcode] text on a page [/url_shortcode] to link.
– or – Here is some [url_field_shortcode anchortext=”text on a page” rel=”nofollow”] to link.
Your image field shorcode also lacks these kinds of attributes for things like alt text or captions in the same way. These are minor adjustments that would make these fields far more useful than just showing the text of a url or the image without any other alignment, captioning or size capabilities enabled.
When using a standard image shortcde in WP, you can wrap the image shortcode with a caption shortcode. This doesn’t work on your image field and there are no attributes enabled to support this within the field type itself.
In this example from the WP Codex, you can see the caption, alignment options, etc. available in WP natively that are not enabled in your image field.
[caption id="attachment_6" align="alignright" width="300"] image [/caption]
Here’s the example from codex for more explanation:
Because all of the field html is sanitized and there are are no attributes avaiable in the shortcodes, the only useful url field is actually the wysiwyg editor field, since it does provide at least a little bit of control over the link or url being added.
The wysiwyg field is currently the only way to display an image that includes captions, alt text, etc. & has control of basic alignment etc. without having to style everything manually per-field with css.
Even though the raw text/html tab of the wysiwyg editor is disabled and the shortcodes have no supports or attributes available, the image field and url fields are both inferior to the wysiwyg as an image or url field.