Well, UltraEdit/UEStudio is not as optimized as PSPad for web page editing. There is already a discussion about that - see UEdit or PSPAD ???
A macro can be used for selecting the characters between 2 HTML tags as posted at Some questions about functions
. But it is definitively not perfect, especially on nested elements like in your screenshot. If your HTML code is always as perfect indented as in your screenshot an improved macro code could select always the correct matching end tag for the current tag.
But I think locking a selection will never be available in UltraEdit/UEStudio.
You could only temporarily convert the current selection to an alternate comment with different background color and when finished editing in it remove the alternate comments with a macro.
Also you could use the multi-language syntax highlighting feature to highlight a selection temporarily with a different background color. For example if you never use ASP in your HTML files you could copy the whole HTML language definition in your wordfile to an other language number and replace HTML_LANG by ASP_LANG. Then you need a macro which adds before and after current selection the start and end tag for VBScript and a second macro which removes these elements next the current cursor position when "locking" should be disabled.
Both are dirty tricks, but maybe useful for you.
However, feature requests can be always send to IDM.