There are situations where basic shapes do not provide the flexibility you need to achieve a certain effect. Drop shadows, to provide a popular example, cannot be created reasonably with a combination of gradients. Filters are SVG's mechanism to create sophisticated effects.

When SVG was specified, support for web fonts was not widespread in browsers. Since accessing the correct font file is, however, crucial for rendering text correctly, a font description technology was added to SVG to provide this ability. It was not meant for compatibility with other formats like PostScript or OTF, but rather as a simple means of embedding glyph information into SVG when rendered.

The stroke attribute is a presentation attribute defining the color (or any SVG paint servers like gradients or patterns) used to paint the outline of the shape;

A quantifier repeats an atom a certain number of times. The quantifier is placed after the atom it applies to.

The restart attribute specifies whether or not an animation can restart.

The pointsAtZ attribute represents the y location in the coordinate system established by attribute primitiveUnits on the <filter> element of the point at which the light source is pointing, assuming that, in the initial local coordinate system, the positive z-axis comes out towards the person viewing the content and assuming that one unit along the z-axis equals one unit in x and y.

The JavaScript exception "is not iterable" occurs when the value which is given as the right-hand side of for...of, as argument of a function such as Promise.all or TypedArray.from, or as the right-hand side of an array destructuring assignment, is not an iterable object.

The text-rendering attribute provides hints to the renderer about what tradeoffs to make when rendering text.

The JavaScript exception "missing formal parameter" occurs when your function declaration is missing valid parameters.

The side attribute determines the side of a path the text is placed on (relative to the path direction).