[ToDo] Clarify in documentation that `.parent` is an internal property and not reliable on the node API

I'm Writing a ThemeColor Plugin, use Visitor.

In fn:visitColor , node.parent sometimes is null (box-shadow:0 0 0 1px #999 inset). I can't find the parent Declaration Node of Color Node.
so I want to less.js/lib/less/visitors/visitor.js Visitor.prototype.visit, funcOut.call(impl, node); => funcOut.call(impl, node, visitArgs);.
And my Code will be like this.

class ThemeVisitor {
 
    visitDeclaration(node, visitArgs) {
        node.isColorDeclaration = false;
        visitArgs.isColorDeclaration = false;
        return node;
    }

    visitColor(node, visitArgs) {
        visitArgs.isColorDeclaration = true;
        return node;
    }

    visitDeclarationOut(node, visitArgs) {
        if (visitArgs.isColorDeclaration) {
            node.isColorDeclaration = true;
        }
        return node;
    }

    visitRulesetOut(node) {
        node.rules = node.rules.filter((item) => {
            if (item instanceof Declaration) {
                return item.isColorDeclaration;
            }
            if (item instanceof Ruleset) {
                return !!item.rules.length;
            }
        });
        return node;
    }

}

Start with packages/less/src/less/visitors/visitor.js, especially Visitor.prototype.visit, and compare it with the issue's ThemeVisitor example. Update the relevant documentation to clarify that node.parent is an internal, unreliable property on the node API and make the supported behavior clear.