Low-level languages like C, have manual memory management primitives such as malloc() and free(). In contrast, JavaScript automatically allocates memory when objects are created and frees it when they are not used anymore (garbage collection). This automaticity is a potential source of confusion: it can give developers the false impression that they don't need to worry about memory management.

Classes are a template for creating objects. They encapsulate data with code to work on that data. Classes in JS are built on prototypes but also have some syntax and semantics that are unique to classes.

The const declaration declares block-scoped local variables. The value of a constant can't be changed through reassignment using the assignment operator, but if a constant is an object, its properties can be added, updated, or removed.

The null keyword refers to the null primitive value, which represents the intentional absence of any object value.

The <animate> SVG element provides a way to animate an attribute of an element over time.

The <ellipse> SVG element is an SVG basic shape, used to create ellipses based on a center coordinate, and both their x and y radius.

The href attribute defines a link to a resource as a reference URL. The exact meaning of that link depends on the context of each element using it.

The JavaScript exception "missing = in const declaration" occurs when a const declaration was not given a value in the same statement (like const RED_FLAG;). You need to provide one (const RED_FLAG = true).

The JavaScript exception "is not a constructor" occurs when there was an attempt to use an object or a variable as a constructor, but that object or variable is not a constructor.

The patternUnits attribute indicates which coordinate system to use for the geometry properties of the <pattern> element.