In order to mark an editor as active, one clicks into the document itself or onto its header. However, clicking into the “white space” on either side of the editiable area of the document in the editor window does not highlight that editor. I find this confusing. Multiple times I’ve clicked in this white space to highlight an editor and changed docs only to find it opens in the other editor (yes, I know the blue title bar marks the currently selected editor). One should be able to click anywhere in the window of the editor in split mode to select it.