I could not verify if following really works, but give it a try:

• Start UltraEdit and paste into a new file following lines:
  

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  REGEDIT4
  
  [HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\View Source Editor\Editor Name]
  @="\"C:\\Program Files (x86)\\IDM Computer Solutions\\UltraEdit\\uedit32.exe\""

  Modify the path to uedit32.exe if you have UltraEdit not installed into the default directory.
• Save the file for example with name UltraEditViewSourceEditorAdd.reg.
• Double click on this file to import the data to Windows registry. You must confirm making this modification with using temporarily administrator privileges and confirm the import of the data.
• Start now Internet Explorer 11 if not already running and try if with a right click on a displayed page and left click on View Source from the context menu results in displaying the source of the HTML file in UltraEdit.

This works for Internet Explorer 8 on Windows XP SP3. Internet Explorer 10 and 11 are not available for Windows XP which is the reason why I could not verify currently my instructions.

I want to write also the opposite. Remove UltraEdit as viewer for HTML source in Internet Explorer:

• Start UltraEdit and paste into a new file following lines:
  

  Code: Select all

  REGEDIT4
  
  [-HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\View Source Editor]

• Save the file for example with name UltraEditViewSourceEditorRemove.reg.
• Double click on this file to import the data to Windows registry. You must confirm making this modification with using temporarily administrator privileges and confirm the import of the data which in real removes the entire registry key View Source Editor.

The modification is immediately active and therefore using View Source from context menu of a page results in displaying the source again with built-in source viewer of IE.

I researched a little in WWW and found out that for IE8, IE9 and IE10 it is possible to select the application for viewing the source of a page without modifying the registry manually. According to Getting Started with the F12 Developer Tools in IE9 and Navigating the F12 Developer Tools Interface in IE10 all needed to do is

• pressing key F12 to open the developer tools window,
• opening from menu File the submenu Customize Internet Explorer view source,
• clicking on menu item Other and browsing to Uedit32.exe.

But according to What's new in F12 Tools in IE11 the developer tools are rebuilt from the ground up in IE11. I found nothing in Using the F12 developer tools in IE11 nor anywhere else about customization of source viewer application. It might be not possible anymore to customize which application is used for viewing the source of an HTML file.

Perhaps you have no other choice than selecting in the Internet Options on tab Programs UltraEdit Professional Text/Hex Editor as default HTML editor, and Show the menu bar in Internet Explorer, and click in menu File on Edit with UltraEdit if you want to view the source of a page in UltraEdit.