Currently, the default pattern that comes up in "Extract Regex" dialog is the pattern `\\[(.*?)
If group 1 is selected and executed on sample data such as ``, it will yield a result of "123". User's should not be burdened with providing escape characters to the regex pattern, as regex patterns are already difficult to read and write. Proper escaping of the user input should be done on the backend, or better on the frontend with syntax feedback to the user (new story?), before compiling the regex pattern.