src/vs/editor/contrib/anchorSelect/browser/anchorSelect.ts/SelectionAnchorController/setSelectionAnchor
class SelectionAnchorController:	setSelectionAnchor(): void {
		if (this.editor.hasModel()) {
			const position = this.editor.getPosition();
			const previousDecorations = this.decorationId ? [this.decorationId] : [];
			const newDecorationId = this.editor.deltaDecorations(previousDecorations, [{
				range: Selection.fromPositions(position, position),
				options: {
					description: 'selection-anchor',
					stickiness: TrackedRangeStickiness.NeverGrowsWhenTypingAtEdges,
					hoverMessage: new MarkdownString().appendText(localize('selectionAnchor', "Selection Anchor")),
					className: 'selection-anchor'
				}
			}]);
			this.decorationId = newDecorationId[0];
			this.selectionAnchorSetContextKey.set(!!this.decorationId);
			alert(localize('anchorSet', "Anchor set at {0}:{1}", position.lineNumber, position.column));
		}
	}