Add comprehensive Chinese documentation and Emacs Lisp implementation for CSS selector parser

[Copilot]

Provides detailed Chinese technical documentation explaining the CSS selector parsing implementation and a complete Emacs Lisp reimplementation of the parser core.

Documentation (2,327 lines)

• CSS选择器解析器实现详解.md (943 lines): Deep dive into tokenization and parsing algorithms, escape sequence handling, recursive descent parsing, and complete parsing flow with examples
• CSS解析器使用指南.md (505 lines): API reference, usage patterns, and 15 practical examples
• README-CN.md: Quick start guide and feature overview

Emacs Lisp Implementation (1,135 lines)

css-selector-parser.el implements:

• Full tokenizer with escape sequence support (hex and character escapes)
• Recursive descent parser generating typed AST nodes
• 12 node types: tag, class, id, attribute, pseudo, combinator, universal, nesting, comment, string, selector, root
• Tree walking APIs with type-specific iterators

examples.el demonstrates:

;; Parse and extract classes
(css-selector-parse "div.header > nav.menu")
;; => AST with tag, class, combinator nodes

;; Type-specific traversal
(css-selector-walk-classes ast 
  (lambda (node) 
    (plist-put node :value (concat "prefix-" (plist-get node :value)))))

;; Serialize back to CSS
(css-selector-stringify ast)
;; => "div.prefix-header > nav.prefix-menu"

Supports: basic selectors, combinators (descendant, child, adjacent, sibling), pseudo-classes/elements, attribute selectors (basic operators), nesting, comments.

Implementation Notes

Educational focus prioritizes code clarity over completeness. Limitations documented:

• Attribute selectors: basic operators only
• Pseudo-classes: no parameter parsing (:nth-child() etc.)
• Namespace handling simplified

Original prompt

对CSS选择器解析部分梳理成详细的中文文档帮我理解是如何实现的，并且用 emacs-lisp 代码来重新实现这部分内容。

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