Current implementation of Text UI automation pattern doesn't support obtaining the attributes of the selection, e.g. bold, italic, etc.

The API allows returning custom ITextRangeProvider where the behavior could be implemented , but this requires a lot of work. 

If this is built-in, the API will allow getting the attributes as follows:

            var automationPeer = (RadRichTextBoxAutomationPeer)FrameworkElementAutomationPeer.FromElement(this.radRichTextBox);
            TextPattern textPattern = (TextPattern)automationPeer.GetPattern(PatternInterface.Text);

            object isItalic = textPattern.GetSelection()[0].GetAttributeValue(TextPattern.IsItalicAttribute);
            if (isItalic == TextPattern.MixedAttributeValue)
            {
                // mixed
            }
            else
            {
                bool italic = (bool)isItalic;
            }

Currently, AutomationElement.NotSupported is always returned.