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