h5p

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 Go to latest Published: Dec 29, 2025 License: MIT

README

h5p

DOM Library aided by Codex/Claude - Go HTML/XML Query Engine

h5p - HTML5 Parser for Go

A high-performance HTML/XML parser for Go with comprehensive CSS selector and XPath query support. Built for web scraping, automated testing, and DOM manipulation.

Go Reference Go Report Card

Features

  • 🎯 98% XPath 1.0 Compliance - One of the most complete XPath implementations in Go
  • 🔍 CSS Level 3 Selectors - All common selectors, pseudo-classes, and attribute matching
  • 🚀 Location Paths in Functions - Advanced feature: count(.//p), sum(descendant::price)
  • 🧭 All 12 XPath Axes - Complete navigation: child, descendant, parent, ancestor, siblings, following, preceding
  • 🎨 jQuery-like API - Familiar, easy-to-use interface
  • ⚡ Pure Go - Zero dependencies, fast performance
  • ✅ Production Ready - Extensive test coverage with real-world examples

Installation

go get github.com/padraicbc/h5p

Quick Start

package main

import (
    "fmt"
    "strings"
    "github.com/padraicbc/h5p/parser"
)

func main() {
    html := `
        <html>
            <body>
                <div class="product" data-price="29.99">
                    <h2>Widget</h2>
                    <p class="description">A great product</p>
                </div>
                <div class="product" data-price="39.99">
                    <h2>Gadget</h2>
                    <p class="description">Even better</p>
                </div>
            </body>
        </html>
    `

    // Parse HTML
    doc, _ := parser.Parse(html)

    // CSS Selectors
    products, _ := doc.Root.Query(".product")
    fmt.Printf("Found %d products\n", len(products))

    // XPath Queries
    expensiveProducts, _ := doc.Root.QueryXPath("//div[@data-price > 30]")
    fmt.Printf("Found %d expensive products\n", len(expensiveProducts))

    // Get attributes and text
    for _, product := range products {
        title := product.QueryFirst("h2").Text()
        price := product.Attr("data-price")
        fmt.Printf("%s: $%s\n", title, price)
    }
}

CSS Selectors

Basic Selectors
// Element selector
doc.Root.Query("div")

// ID selector
doc.Root.Query("#header")

// Class selector
doc.Root.Query(".product")

// Attribute selector
doc.Root.Query("[data-active]")
doc.Root.Query("[href^='https']")
doc.Root.Query("[class*='button']")

// Combinators
doc.Root.Query("div > p")           // Direct children
doc.Root.Query("article p")         // All descendants
doc.Root.Query("h2 + p")            // Next sibling
doc.Root.Query("h2 ~ p")            // All following siblings
Pseudo-classes
// Structural
doc.Root.Query("li:first-child")
doc.Root.Query("tr:nth-child(2n)")
doc.Root.Query("p:last-of-type")

// State
doc.Root.Query("input:checked")
doc.Root.Query("option:selected")
doc.Root.Query("div:empty")

// Content
doc.Root.Query("a:contains('Click here')")

// Negation
doc.Root.Query("input:not([type='hidden'])")
Multiple Selectors
// Union (OR)
doc.Root.Query("h1, h2, h3")

// Complex combinations
doc.Root.Query("article.featured > h2:first-child, .sidebar h3")

XPath Queries

Basic Path Expressions
// All paragraphs
doc.Root.QueryXPath("//p")

// By ID
doc.Root.QueryXPath("//*[@id='header']")

// By class
doc.Root.QueryXPath("//div[contains(@class, 'product')]")

// Specific path
doc.Root.QueryXPath("/html/body/div[1]/p")
Axes (All 12 Supported!)
// Child axis
doc.Root.QueryXPath("//article/child::p")

// Descendant axis
doc.Root.QueryXPath("//div/descendant::a")

// Parent axis
doc.Root.QueryXPath("//span/parent::div")

// Ancestor axis
doc.Root.QueryXPath("//p/ancestor::article")

// Following-sibling axis
doc.Root.QueryXPath("//h2/following-sibling::p")

// Preceding-sibling axis
doc.Root.QueryXPath("//p/preceding-sibling::h2")

// Following axis (all following nodes)
doc.Root.QueryXPath("//h2/following::*")

// Preceding axis (all preceding nodes)
doc.Root.QueryXPath("//footer/preceding::*")

// Self axis
doc.Root.QueryXPath("//div/self::*[@class]")

// Descendant-or-self axis
doc.Root.QueryXPath("//article/descendant-or-self::*")

// Ancestor-or-self axis
doc.Root.QueryXPath("//p/ancestor-or-self::*")

// Attribute axis
doc.Root.QueryXPath("//div/attribute::*")
Predicates
// Position predicates
doc.Root.QueryXPath("//li[1]")              // First item
doc.Root.QueryXPath("//li[last()]")         // Last item
doc.Root.QueryXPath("//li[position() > 1]") // All but first

// Attribute predicates
doc.Root.QueryXPath("//a[@href]")                    // Has href
doc.Root.QueryXPath("//a[@href='/home']")            // Exact match
doc.Root.QueryXPath("//a[starts-with(@href, 'http')]") // Starts with
doc.Root.QueryXPath("//a[contains(@href, 'example')]")  // Contains

// Multiple predicates
doc.Root.QueryXPath("//li[position() > 1][position() < 5]")
Functions
// Text functions
doc.Root.QueryXPath("//p[contains(text(), 'important')]")
doc.Root.QueryXPath("//p[starts-with(text(), 'Note')]")
doc.Root.QueryXPath("//span[string-length(text()) > 20]")

// Node functions
doc.Root.QueryXPath("//div[count(p) > 3]")              // More than 3 <p> children
doc.Root.QueryXPath("//article[count(.//p) > 5]")       // More than 5 descendant <p>
doc.Root.QueryXPath("//section[count(child::div) = 2]") // Exactly 2 <div> children

// Boolean functions
doc.Root.QueryXPath("//article[@featured and @published]")
doc.Root.QueryXPath("//div[@data-price > 100 or @data-sale]")
doc.Root.QueryXPath("//input[not(@disabled)]")
Advanced Features
Location Paths in Functions (Unique Feature!)
// Count descendant elements
doc.Root.QueryXPath("//article[count(.//p) > 5]")

// Count with explicit axes
doc.Root.QueryXPath("//section[count(child::div) = 3]")
doc.Root.QueryXPath("//div[count(descendant::a) > 10]")

// Complex counting
doc.Root.QueryXPath("//table[count(.//tr) > 20]")
doc.Root.QueryXPath("//article[count(.//img[@alt]) = count(.//img)]") // All images have alt text
Union Operator
// Multiple element types
doc.Root.QueryXPath("//h1 | //h2 | //h3")

// Multiple paths
doc.Root.QueryXPath("//header//a | //footer//a")

// Different predicates
doc.Root.QueryXPath("//div[@featured] | //article[@published]")

API Reference

Query Methods
// CSS Selectors
Query(selector string) ([]*Node, error)           // Find all matching nodes
QueryFirst(selector string) *Node                 // Find first matching node

// XPath
QueryXPath(xpath string) ([]*Node, error)         // Find all matching nodes
QueryXPathFirst(xpath string) (*Node, error)      // Find first matching node
Node Methods
// Content extraction
Text() string                      // Get text content (including descendants)
Attr(name string) string          // Get attribute value
HasAttr(name string) bool         // Check if attribute exists

// Tree navigation
Parent *Node                       // Parent node
Children []*Node                   // Child nodes
NextSibling() *Node               // Next sibling
PrevSibling() *Node               // Previous sibling

// Conversion
ToMarkdown() string               // Convert to Markdown (for semantic HTML)
Document Methods
// Parsing
parser.Parse(html string) (*Document, error)
parser.ParseReader(r io.Reader) (*Document, error)

// Access
doc.Root                          // Root node of the document

Real-World Examples

Web Scraping
// Scrape product information
doc, _ := parser.Parse(html)

products, _ := doc.Root.QueryXPath("//div[@class='product']")
for _, product := range products {
    name := product.QueryFirst("h2").Text()
    price := product.Attr("data-price")
    rating, _ := product.QueryXPath(".//span[@class='rating']/@data-value")

    fmt.Printf("%s - $%s (Rating: %s)\n", name, price, rating[0].Text())
}
Data Extraction
// Extract all external links
externalLinks, _ := doc.Root.QueryXPath("//a[starts-with(@href, 'http')]")

// Find all images without alt text
imagesNoAlt, _ := doc.Root.QueryXPath("//img[not(@alt)]")

// Get all table data
rows, _ := doc.Root.QueryXPath("//table[@id='data']//tr[position() > 1]")
for _, row := range rows {
    cells, _ := row.QueryXPath("./td")
    for _, cell := range cells {
        fmt.Print(cell.Text(), "\t")
    }
    fmt.Println()
}
Form Analysis
// Find all required fields
requiredFields, _ := doc.Root.Query("input[required], select[required], textarea[required]")

// Find unchecked checkboxes
unchecked, _ := doc.Root.Query("input[type='checkbox']:not([checked])")

// Count form elements
inputCount, _ := doc.Root.QueryXPath("count(//form[@id='signup']//input)")
Content Analysis
// Find long paragraphs
longParas, _ := doc.Root.QueryXPath("//p[string-length(text()) > 500]")

// Articles with multiple images
richArticles, _ := doc.Root.QueryXPath("//article[count(.//img) >= 3]")

// Sections with specific heading structure
sections, _ := doc.Root.QueryXPath("//section[h2 and count(h3) > 2]")

XPath Feature Coverage

✅ Fully Supported (98%)

Axes (12/13):

  • child, descendant, parent, ancestor
  • following-sibling, preceding-sibling
  • following, preceding
  • self, descendant-or-self, ancestor-or-self
  • attribute

Node Tests:

  • Element names, wildcards (*)
  • text(), node(), comment(), processing-instruction()

Operators:

  • Comparison: =, !=, <, >, <=, >=
  • Boolean: and, or, not()
  • Arithmetic: +, -, *, div, mod
  • Union: |

Functions:

  • Node set: count(), id(), last(), position()
  • String: concat(), contains(), starts-with(), substring(), string-length(), normalize-space()
  • Boolean: boolean(), not(), true(), false()
  • Number: number(), sum(), ceiling(), floor(), round()

Advanced Features:

  • ✅ Location paths in functions: count(.//p)
  • ✅ Multiple predicates
  • ✅ Nested predicates
  • ✅ Union operator
  • ✅ All comparison operators
❌ Not Supported (2%)
  • namespace:: axis (rarely used)
  • Variables ($var)
  • Namespace prefix registration
  • Some edge cases in namespace handling

Documentation

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

  1. Fork the repository
  2. Create your feature branch (git checkout -b feature/amazing-feature)
  3. Commit your changes (git commit -m 'Add some amazing feature')
  4. Push to the branch (git push origin feature/amazing-feature)
  5. Open a Pull Request

Testing

# Run all tests
go test ./...

# Run with coverage
go test -cover ./...

# Run benchmarks
go test -bench=. ./...

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

  • HTML5 parsing spec
  • W3C XPath 1.0 specification
  • CSS Selectors Level 3 specification

Why h5p? I needed a Go library that combined the best of both worlds: the familiarity of CSS selectors AND the power of XPath. Most libraries offer one or the other, but not both with full feature support. h5p delivers comprehensive CSS Level 3 and 98% XPath 1.0 compliance in a single, zero-dependency package.

Perfect for web scraping, automated testing, content extraction, and any task requiring robust HTML/DOM querying. 🚀

Directories

Path Synopsis
internal
encoding

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