I changed the input file now - I added whitespaces after the Group number - now the function list looks perfect

Well, that’s the ultimate situation, when you have control over the data. Much more often, the format is dictated to you.

Had we known that, we’d have advised you to just change your format before even discussing how the tab might be playing in the function list.

Group 04 Some Text

BR,
Ninon

If the application is just sending the raw text to the treeview widget (or whatever widget is being used in that panel), and the widget itself is just choosing not to display the tab…

A quick look at the source code seems to indicate that is the case.

It seems a bit ambitious; if it were me, I’d probably accept how it shows currently.

Whether or not it’s ambitious probably depends on the current implementation. If the application is just sending the raw text to the treeview widget (or whatever widget is being used in that panel), and the widget itself is just choosing not to display the tab, then there might not be much that the developer can do about it. But if the application is removing tabs before sending the function names to the widget, then instead of removing them, I would suggest just replacing with a single space (which I would think would be just as easy as removing them).

As the documentation says, you cannot change/replace characters

Specifically, it says so HERE.

the Function List doesn’t display a tab as you might expect

It appears to display nothing for the tab position. Not sure what it should display; probably it should look up the number of spaces for the current “language” of the source file, and insert multiple spaces? It seems a bit ambitious; if it were me, I’d probably accept how it shows currently.

Is there a way to include a space after the number

As the documentation says, you cannot change/replace characters in the Function List panel; you can just choose which characters from the file match and get displayed.

There is a tab character in your file … and unfortunately, the Function List doesn’t display a tab as you might expect. For that, you might want to file a bug report following the instructions in the FAQ

It’s regular expression “regex” syntax, and the function list docs aren’t going to repeat what’s already elsewhere in the manual.

Looking at your main expression:

Group\s+\w*[0-9]\t*[A-Za-z_\x7F-\xFF][\w\x7F-\xFF]*
^^^^^^^^~~~~~~~~^^^~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
(1)     (2)     (3)(4)               (5) 

1. literal “Group” followed by one or more space characters
2. zero or more alphanumeric+underscore, followed by exactly one digit from 0-9
3. zero or more tabs
4. one character that is uppercase, lowercase, underscore, or extended-ASCII range
5. zero or more characters that are alphanumeric+underscore or extended-ASCII

With the expression you supplied, I would expect it to work.

And, in fact, when I tried it, it did work (or, at least, mostly):

FILE (with UDL=“Example_sensors” selected)

Group 04	Some Text
	text 1
	text 2
	text 3
	text 4
	text 5

example_sensors.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<!-- ==========================================================================\
|
|   To learn how to make your own language parser, please check the following
|   link:
|       https://npp-user-manual.org/docs/function-list/
|
\=========================================================================== -->
<NotepadPlus>
	<functionList>
		<!-- ================================ [ Batch / Command Shell Script ] -->

		<parser
			displayName="Batch / Command Shell Script"
			id         ="batch_label"
			commentExpr="(?x)                                               # Utilize inline comments (see `RegEx - Pattern Modifiers`)
							(?m-s:(?i:REM)(?:\h.+)?$)                       # Single Line Comment 1
						|	(?m-s::{2}.*$)                                  # Single Line Comment 2
						"
		>
			<function
				mainExpr="Group\s+\w*[0-9]\t*[A-Za-z_\x7F-\xFF][\w\x7F-\xFF]*"
			/>
		</parser>
	</functionList>
</NotepadPlus>

overrideMap.xml (snippet):

			<!-- ==================== User Defined Languages ============================ -->
			<association id= "example_sensors.xml"				userDefinedLangName="Example_sensors"/>

I said “mostly”, because it only grabbed “Some”, not “Some Text”, because “Some Text” has a space in it, and your regex never allowed spaces, so it obviously couldn’t go any farther. If I were doing it, I would simplify it down to (?-s)Group\h+\w*[0-9]\t*.*, which will grab everything on that line after the optional tab