function getIndentText(text, node) {
	return leadingWhitespaceRegex.exec(
		text.slice(getBeginningOfLineOffset(node)),
	)[0];
}
Gets the leading text, typically whitespace with possible blockquote chars,
used to indent a code block.
@param {string} text The text of the file.
@param {Node} node A Markdown code block AST node.
@returns {string} The text from the start of the first line to the opening
    fence of the code block.