When you choose “Go to Line” in the Find menu, or press Command-L, CotEditor displays the Go To dialog box to give you quick access to the line(s) you want to see.
In the dialog box, enter the line number, and click “Go”.
If you type in “3”:
=> The line 3 (the third line from the top) will be selected.
If you type in “3:2”:
=> What this indicates is “starting from line 3, select 2 lines.” Thus, the line 3 and 4 will be selected.
If you type in “3:-1”:
=> What this indicates is “starting from line 3, select the rest lines except the last 1 line.” Thus, if the document has 10 lines, the lines from the line 3 to 9 will be selected.