Add helper functions for working with ASTs

Node creation

ArrowCSS_CreateDeclaration(ast, property, value) for creating a declaration with a property-value pair
ArrowCSS_CreateAtRule to create an at-rule
ArrowCSS_CreateRuleset(ast, selector) for creating a ruleset with a specific selector.
ArrowCSS_CloneNode to to clone an ASTNode struct along with all of its children.

Tree modification

To append a child to a node, ArrowCSS_AppendChild can be used which will validate the passed nodes and add the child node to the linked list of children under the parent node.

To add a child after another child in a linked list, ArrowCSS_InsertAfter(target, newNode) which will insert the newNode after the target node as a child of the parent node.

To add a child before another child in a linked list of children, ArrowCSS_InsertBefore(parent, target,newNode) which will insert the newNode before the target node as a child of the parent node.

To remove a child node, ArrowCSS_RemoveChild(ast, child) will remove the provided child node from the ast and will return the removed child node to the caller.

Traversal

Traversal: ArrowCSS_Walk(root, callback, userData) which will allow the user to traverse the tree using a custom callback function for each node as well as being able to pass their own data such as state or config

Search/query

Get declaration from block: ArrowCSS_GetDeclaration(ruleset, propertyName) to find and return the declaration with the given property name within the block or NULL if the declaration is not found.
Check if a selector is present for a ruleset: ArrowCSS_GetSelector(ruleset, selector) to check if a specific selector exists within the selector for a ruleset.

String view helper functions

Equals: ArrowCSS_ViewEquals(view,string) efficiently compares whether a string is the same as the string within a string view.
Starts with: ArrowCSS_ViewStartsWith(view, string) checks whether a string view starts with a substring
Contains: ArrowCSS_ViewContains(view,string) checks whether a string view contains a substring
Update: ArrowCSS_ViewUpdate(ast, targetView, string) updates a string view to contain a new string as string views cannot be directly modified

Start by locating the ASTNode structure, its child linked-list representation, and the existing string-view utilities. Then trace how nodes are created and freed before planning the requested creation, cloning, tree-editing, traversal, query, and view helpers. Done means each listed ArrowCSS helper is implemented with the stated behavior and validated by the project's existing checks.