The font-size-adjust attribute allows authors to specify an aspect value for an element that will preserve the x-height of the first choice font in a substitute font.

An expression statement is an expression used in a place where a statement is expected. The expression is evaluated and its result is discarded — therefore, it makes sense only for expressions that have side effects, such as executing a function or updating a variable.

The d attribute defines a path to be drawn.

The by attribute specifies a relative offset value for an attribute that will be modified during an animation.

The logical OR (||) (logical disjunction) operator for a set of operands is true if and only if one or more of its operands is true. It is typically used with boolean (logical) values. When it is, it returns a Boolean value. However, the || operator actually returns the value of one of the specified operands, so if this operator is used with non-Boolean values, it will return a non-Boolean value.

The font-variant attribute indicates whether the text is to be rendered using variations of the font's glyphs.

The logical AND assignment (&&=) operator only evaluates the right operand and assigns to the left if the left operand is truthy.

Method definition is a shorter syntax for defining a function property in an object initializer. It can also be used in classes.

The JavaScript exception "missing : after property id" occurs when objects are created using the object initializer syntax. A colon (:) separates keys and values for the object's properties. Somehow, this colon is missing or misplaced.

The v-mathematical attribute indicates the alignment coordinate for glyphs to achieve mathematical baseline alignment for vertically oriented glyph layouts. The value is an offset in the font coordinate system relative to the glyph-specific vert-origin-x attribute.