更改HTML文本框:覆盖而不是作为用户类型插入

我正在开发一种允许编辑文本的服务.为了帮助用户进行此过程，我希望允许用户将文本字段设置为覆盖模式(如Word等).如何将HTML文本框的行为更改为覆盖而不是插入文本用户输入的类型?

I am working on a service which will allow editing of text. To aid the user in the process, I'd like to allow the user to set a text field to overwrite mode, as is possible in Word, etc. How can the behaviour of an HTML text box be changed to overwrite instead of insert text as the user types?

例如，如果文本框中包含以下文本:

For example, if the textbox had the text:

This is a trst.

用户可以在r和t之间单击，键入一个e，然后输入文本

The user could click between the r and the t, type a single e and the text would then be

This is a test.

，光标位于e和s之间.我目前使用的是jQuery，因此首选使用那个或纯JavaScript的方法.但是，我会接受任何合理的解决方案.

with the cursor between the e and the s. I'm currently using jQuery, so methods using either that or pure javascript would be preferred. I would accept any reasonable solution, however.