src/MarkdownFactory.php
public function addBlockPlugin($firstLetter, $blockName)
    {
        if (!\is_string($blockName)) {
            throw new ParameterNotAllowedException('$blockName should be type of string');
        }

        if (!isset($this->blockPlugins[$firstLetter]) || !in_array($blockName, $this->blockPlugins[$firstLetter], true)) {
            $this->blockPlugins[$firstLetter][] = $blockName;
        }

        return $this;
    }
public function addBlockPlugin($firstLetter, $blockName)
    {
        if (!\is_string($blockName)) {
            throw new ParameterNotAllowedException('$blockName should be type of string');
        }

        if (!isset($this->blockPlugins[$firstLetter]) || !in_array($blockName, $this->blockPlugins[$firstLetter], true)) {
            $this->blockPlugins[$firstLetter][] = $blockName;
        }

        return $this;
    }
@param string $firstLetter
@param string $blockName

@throws ParameterNotAllowedException

@return $this