Given a tree, it creates a flattened one by merging the keys and binding the leaf values to the new keys.

It also transforms camelCase names into kebab-case and substitutes ‘/’ by ‘-‘.

This is thought to be useful to generate CSS Custom Properties from a tree, although there’s nothing in the implementation of this function that requires that format.

For example, assuming the given prefix is ‘–wp’ and the token is ‘–‘, for this input tree:

{
  'some/property': 'value',
  'nestedProperty': {
    'sub-property': 'value'
  }
}

it’ll return this output:

{
  '--wp--some-property': 'value',
  '--wp--nested-property--sub-property': 'value'
}

$tree array Required

Input tree to process.

$prefix string Optional

Prefix to prepend to each variable.

Default: ''

$token string Optional

Token to use between levels. Default '--'.

Default: '--'

array The flattened tree.

File: wp-includes/class-wp-theme-json.php. View all references

protected static function flatten_tree( $tree, $prefix = '', $token = '--' ) {
	$result = array();
	foreach ( $tree as $property => $value ) {
		$new_key = $prefix . str_replace(
			'/',
			'-',
			strtolower( _wp_to_kebab_case( $property ) )
		);

		if ( is_array( $value ) ) {
			$new_prefix = $new_key . $token;
			$result     = array_merge(
				$result,
				static::flatten_tree( $value, $new_prefix, $token )
			);
		} else {
			$result[ $new_key ] = $value;
		}
	}
	return $result;
}