The following methods use an int to represent a search character:
When I see an int representing a character, I tend to assume the method can handle supplementary characters. However, the current behaviour of these methods depends upon whether the CharSequence is a String or not.
The Javadoc for these methods are ambiguous on this point, stating:
This method uses String.lastIndexOf(int) if possible.
I think we should consider updating the CharSequenceUtils methods used by this class to convert all CharSequence parameters to strings, enabling full code point support. The docs could be updated to make this crystal clear.
There is a question of whether this breaks backwards compatibility.