Problem with regex in text Mapping

[pico977]

Hi,
I am making a panel and I need to change the label text of a connector.
I made the model with draft.io, and the label is set with the text "GE":

<mxCell id="myID_10" value="GE" ...

So I made a rule to change the content of the label, and this works.
The value represented in the label can be negative or positive, and I want the connector color to change based on the sign.
I configured a threshold with condition "value" set to "/.-./" and then I configured the "color mapping" and this also works fine.
The last step is to represent the absolute value of the number in the label.
I thought about using the "Label / text Mappings" function:

WHAT: myID_10
WHEN: When Metric Displayed
HOW: Substring
WITH: /[^-]/

But this doesn't work!
Do you have any suggestions?