Previously, all attributes were allowed except for "style" & "on*".
Now, all attributes are restricted except for those added to whitelist ("style" & "on*" are still prohibited).
However, "dir" & "lang" are always allowed and do not need to be added to the whitelist.
Any other attributes need to be added to the whitelist.
The whitelist allows wildcard support.
Example:
Before, this was the default value "allowed_html" = "<a> <em> <strong> <cite> <blockquote> <code> <ul> <ol> <li> <dl> <dt> <dd> <h2> <h3> <h4> <h5> <h6>"
After the change, this is the default value for Basic HTML format "allowed_html" = "<a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul> <ol start type='1 A I'> <li> <dl> <dt> <dd> <h2 id> <h3 id> <h4 id> <h5 id> <h6 id>
If you want to add in a wildcard to the class attribute for any value starting with "align-" for h6 use this:
<h6 id class="align-*">
Wildcards are also allowed for custom attribute names.
The filter name was changed from "Limit allowed HTML tags" to "Limit allowed HTML tags and correct faulty HTML".
The filter "Correct faulty and chopped off HTML" is no longer enabled by default for Basic and Restricted HTML formats. After this change, the HTML filter will automatically do this for you.
If you have an existing D8 site prior to this change, you may have to add attributes to the allowed HTML.