在WPF RichTextBox Control中获取单词光标的方法是打开的

I would like to know how I can get the word that current cursor is on, in WPF RichTextBox. I am aware that RichTextBox has Selection Property. However, this only gives me the text that is highlighted in the RichTextBox. Instead I would like to know the word the cursor is on even if the whole word is not highlighted. I would like to know how I can get the word t