Form element parsing and DOM interfaces #147

Summary#

Add HTML form-related elements to the parser and DOM tree, and implement their DOM interfaces.

Elements to support#

• <form> → HTMLFormElement
• <input> → HTMLInputElement (types: text, password, checkbox, radio, submit, reset, hidden, number, email, url, search, tel)
• <textarea> → HTMLTextAreaElement
• <select> → HTMLSelectElement
• <option> → HTMLOptionElement
• <optgroup> → HTMLOptGroupElement
• <button> → HTMLButtonElement
• <label> → HTMLLabelElement
• <fieldset> → HTMLFieldSetElement
• <legend> → HTMLLegendElement

Acceptance criteria#

• HTML parser tokenizes and tree-builds all listed elements correctly
• DOM nodes expose element-specific attributes (e.g., input.type, input.value, input.name, form.action, form.method, textarea.rows, select.multiple)
• HTMLFormElement.elements returns a collection of associated form controls
• HTMLInputElement.form, HTMLSelectElement.form, etc. return the owning form
• <label> for attribute resolves to the labeled control
• Unit tests cover parsing and attribute access for each element type

Notes#

This is the foundation issue for Phase 16. All other form issues depend on this.