HTML attributes in uppercase show error in widgets

[sudhir600]

(1) How to reproduce
go to p-admin/widgets.php and add custom HTML.
in custom html box if i add this html, it will error.

<div id="abcd" DATA-HREF="xerjss"></div>

(2) Error - the attribute name of [ "DATA-HREF" ] must be in lowercase.

(3) Why need this
some ad providers (such as flipkart) supply code where attributes are uppercase.

[FlorianBrinkmann]

I am having the same issue: I tried to add an SVG with the viewBox attribute, but am not able to save it because of the »error«.

[navjotjsingh]

Can anyone take a look at this? Even I am having the same problem as @FlorianBrinkmann with using SVG code.

[Nomadsteam]

Same issue here. Cannot save an HTML widget with attribute "viewBox" (WP 5.7).
Error: The attribute name of [ viewBox ] must be in lowercase.

[sabernhardt]

disabling the attr-lowercase rule

[sabernhardt]

47976.diff​ simply disables the error for uppercase letters in attributes.

If the error is important to keep for most situations, the attr-lowercase rule could have an array of specific exceptions instead:

['viewBox', 'DATA-HREF']

​HTMLHint user guide

[simkog]

This is issue is still there when you use the Classic Widgets (​https://wordpress.org/plugins/classic-widgets/) plugin.