CKEditor - Use Existing Functionality

Hello,

I want to know if there is any way I can mimic the functionality of existing toolbar button like Bold, Italic etc.

My requirement is same as what bold is doing, only difference is

1) instead of <b> tag, i want to surround selected text with <Custom_Tag> 

2) Also, I want to get one value from user on pop up which i want to place as attribute in <Custom_Tag>

I know first part can be done by changing value of coreStyles_bold and supplying custom_tag instaead of <b>.

But for 2nd part I have to write plugin which launch pop up and get value. Only issue is when we write plugin, we have to take care of capturing selected html and pasting new html, which is quite complcated to make it for all browser when we have nested tags are involved. But same functionality is already available in ckeditor.js which basicstyle(bold, underline, etc) are using.

How can i use exiting functinolity from ckeditor.js for new plugin, which help me capturing selected html and replcinig it with my custome html maintaining proper DOM structure and works in all browser ?

any help?

thanks