Class SvgItem

Represents a lightweight wrapper around an SVG DOM element that provides convenient, chainable helpers for common SVG manipulations (attributes, styles, transforms, classes and events).

The class encapsulates an underlying SVGElement and exposes methods that operate directly on that element while allowing fluent chaining.

Key behaviors:

• Creation: instances are constructed with the local name of the SVG tag (e.g. "rect", "circle", "g") and internally create the element in the SVG namespace.
• Attribute management: getAttr, getNumAttr, and setAttr let you read and write attributes. Passing null or undefined to setAttr removes the attribute.
• Styling: setStyle assigns CSS properties on the element. When a numeric value is provided, a "px" unit is appended unless the property is known to be unitless (the implementation relies on a small helper to detect unitless properties).
• Geometry & transforms: helpers exist for setting or appending transforms (transform, add_transformation, clear_transform), and higher-level helpers for rotate, translate and scale (both replace and append forms).
• Stroke & fill helpers: stroke, strokeWidth, strokeCap, strokeOpacity, fill, and no_fill provide convenient setters for common paint properties. These methods return this so they can be chained.
• Classes & clipping: addClass / removeClass manipulate the element's class list (supporting space-separated lists) and clip sets a clip-path reference using an id.
• Reset: reset removes all attributes from the element (but does not remove the element itself).
• Events: addDOMEvent attaches DOM events to the underlying element.

Notes and caveats:

• This class is not a full DOM abstraction; it intentionally focuses on a small, ergonomic surface for building and manipulating SVG elements.
• Some behaviors depend on small utility helpers (e.g. numeric/unit detection and event-attachment helpers) provided elsewhere in the codebase.