The JavaScript exception "x is (not) y" occurs when there was an unexpected type. Oftentimes, unexpected undefined or null values.

The media attribute specifies a media query that must be matched for a style sheet to apply.

The limitingConeAngle attribute represents the angle in degrees between the spot light axis (i.e. the axis between the light source and the point to which it is pointing at) and the spot light cone. So it defines a limiting cone which restricts the region where the light is projected. No light is projected outside the cone.

The JavaScript exception ""use strict" not allowed in function" occurs when a "use strict" directive is used at the top of a function with default parameters, rest parameters, or destructuring parameters.

The break statement terminates the current loop or switch statement and transfers program control to the statement following the terminated statement. It can also be used to jump past a labeled statement when used within that labeled statement.

The constructor method is a special method of a class for creating and initializing an object instance of that class.

The JavaScript exception "invalid 'instanceof' operand" occurs when the right-hand side operands of the instanceof operator isn't used with a constructor object, i.e. an object which has a prototype property and is callable.

The JavaScript strict mode-only exception "for-in loop head declarations may not have initializers" occurs when the head of a for...in contains an initializer expression, such as for (var i = 0 in obj). This is not allowed in for-in loops in strict mode. In addition, lexical declarations with initializers like for (const i = 0 in obj) are not allowed outside strict mode either.

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

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.