1-input

foo{{{}}
{{align:center}bar
qux {class:test1,test2}baz{/class}{/align}}

2-output.js

// AST
[ { type: 'text', text: 'foo{{{}}\n{' },
  { type: 'alignment',
    alignment: 'center',
    contents: 
     [ { type: 'text', text: 'bar\nqux ' },
       { type: 'class',
         classNames: [ 'test1', 'test2' ],
         contents: [ { type: 'text', text: 'baz' } ] } ] },
  { type: 'text', text: '}' } ]


// Flattened into individual renderable text elements
[ { type: 'text', text: 'foo{{{}}', tags: [] },
  { type: 'newline' },
  { type: 'text', text: '{', tags: [] },
  { type: 'text',
    text: 'bar',
    tags: [ { type: 'alignment', alignment: 'center', contents: null } ] },
  { type: 'newline' },
  { type: 'text',
    text: 'qux ',
    tags: [ { type: 'alignment', alignment: 'center', contents: null } ] },
  { type: 'text',
    text: 'baz',
    tags: 
     [ { type: 'alignment', alignment: 'center', contents: null },
       { type: 'class',
         classNames: [ 'test1', 'test2' ],
         contents: null } ] },
  { type: 'text', text: '}', tags: [] } ]

3-code.js

'use strict';

module.exports = function splitTextComponents(treeList) {
	function flatten(treeList, tagStack) {
		return treeList.reduce((all, item) => {
			if (item.type === "text") {
				let splitItems = item.text.split("\n").reduce((items, line) => {
					return items.concat([{
						type: "text",
						text: line,
						tags: tagStack
					}, {
						type: "newline"
					}]);
				}, []);

				/* Remove the last newline, because it's not delimiting anything. */
				splitItems.pop();

				return all.concat(splitItems);
			} else {
				return all.concat(flatten(item.contents, tagStack.concat([item])));
			}
		}, []);
	}

	return flatten(treeList, []);
}