BEM Specification

General Format

The BEM structure is composed of a single block followed by zero or more elements.
Each block and element can optionally have modifiers.
The entire structure must occupy the full input without any unexpected or trailing characters or sequences.

A block starts at the beginning of the input.
It is composed of a name optionally followed by modifiers.
The name must start with a lowercase ASCII alphabetic character and can be followed by any combination of ASCII alphanumeric characters. Single dashes are allowed between characters but cannot start or end the name.
Modifiers for a block are enclosed in parentheses and separated by the pipe (|) character. Each modifier also adheres to the naming conventions of blocks.

Each element starts on a new line.
Like blocks, an element is composed of a name optionally followed by modifiers.
The naming convention for elements is the same as blocks: it starts with a lowercase ASCII alphabetic character, followed by any combination of ASCII alphanumeric characters. Single dashes are permitted between characters but not at the beginning or end.
Modifiers for an element are structured in the same way as those for blocks.

media-player(dark)
button(fast-forward|rewind)
timeline

media-player(dark)- Represents a block named media-player with one modifier: dark.
button(fast-forward|rewind) on a new line after a block represents an element named button with two modifiers: fast-forward and rewind.
timeline on another line represents another element named timeline with no modifiers.

The input must start with a block.
Names cannot start or end with dashes and cannot have consecutive dashes.
Modifiers are optional for both blocks and elements.
The entire structure must fit the provided input. There shouldn't be any characters or sequences after the last element.