Form control layout and intrinsic sizing #148

Summary#

Implement layout for form controls as replaced/atomic inline-level elements with intrinsic dimensions.

Details#

Form controls are not normal flow elements — they are atomic inline-level boxes with intrinsic sizes determined by their type and content:

• Text inputs: width from size attribute (default 20 characters), height from font metrics + padding
• Textareas: width from cols attribute (default 20), height from rows attribute (default 2)
• Buttons: sized to fit their content (text label) plus padding
• Checkboxes/radio buttons: small fixed square (e.g., 13x13 CSS px)
• Select dropdowns: width to fit longest option text, height like a single-line text input

Acceptance criteria#

• Form controls participate in inline layout as atomic inline boxes
• Each control type has correct default intrinsic dimensions
• width / height CSS properties override intrinsic sizes
• size attribute on <input> affects intrinsic width
• rows / cols attributes on <textarea> affect intrinsic dimensions
• <fieldset> and <legend> use block layout with correct legend positioning
• Tests verify intrinsic sizing for each control type

Dependencies#

• Form element parsing and DOM interfaces