Add documentation for find_previous_sibling

src/compiler/compile/css/Selector.ts

@@ -470,29 +470,43 @@ function get_element_parent(node: Element): Element | null {
 	return parent as Element | null;
 }
 
-function find_previous_sibling_considering_slots(node: INode): INode {
+/**
+	* Finds the given node's previous sibling in the DOM
+	*	
+	* Unless the component is a custom element (web component), which in this
+	* case, the <slot> element is actually real, the Svelte <slot> is just a 
+	* placeholder and is not actually real. Any children nodes in <slot>
+	* are 'flattened' and considered as the same level as the <slot>'s siblings
+	*
+	* e.g.
+	* <h1>Heading 1</h1>
+	* <slot>
+	*   <h2>Heading 2</h2>
+	* </slot>
+	*
+	* is considered to look like:
+	* <h1>Heading 1</h1>
+	* <h2>Heading 2</h2>
+	*/
+function find_previous_sibling(node: INode): INode {
 	if (node.component.compile_options.customElement) {
 		return node.prev;
 	}
 
 	let current_node: INode = node;
 	do { 
-		// @ts-ignore
 		if (current_node.type === 'Slot') {
-			const slot_children = (current_node as Element).children;
+			const slot_children = current_node.children;
 			if (slot_children.length > 0) {
 				current_node = slot_children.slice(-1)[0]; // go to its last child first
 				continue;
 			}
 		}
 
-		// @ts-ignore
 		while (!current_node.prev && current_node.parent && current_node.parent.type === 'Slot') {
 			current_node = current_node.parent;
 		}
 		current_node = current_node.prev;
-
-	// @ts-ignore
 	} while (current_node && current_node.type === 'Slot');
 
 	return current_node;
@@ -501,7 +515,7 @@ function find_previous_sibling_considering_slots(node: INode): INode {
 function get_possible_element_siblings(node: INode, adjacent_only: boolean): Map<Element, NodeExist> {
 	const result: Map<Element, NodeExist> = new Map();
 	let prev: INode = node;
-	while (prev = find_previous_sibling_considering_slots(prev)) {
+	while (prev = find_previous_sibling(prev)) {
 		if (prev.type === 'Element') {
 			if (!prev.attributes.find(attr => attr.type === 'Attribute' && attr.name.toLowerCase() === 'slot')) {
 				result.set(prev, NodeExist.Definitely);