text: // Markdown-it plugin to render GitHub-style task lists; see
  //
  // https://github.com/blog/1375-task-lists-in-gfm-issues-pulls-comments
  // https://github.com/blog/1825-task-lists-in-all-markdown-documents
  
  markdownitCheckbox = function(md, options) {
  	var defaults;
  	defaults = {
  	  disabled: true,
  	  divWrap: false,
  	  divClass: 'checkbox',
  	  idPrefix: 'cbx_',
  	  ulClass: 'task-list',
  	  liClass: 'task-list-item'
  	};
  	options = Object.assign({}, defaults, options);
  	md.core.ruler.after('inline', 'github-task-lists', function(state) {
  		var tokens = state.tokens;
  		var lastId = 0;
  		for (var i = 2; i < tokens.length; i++) {
  
  			if (isTodoItem(tokens, i)) {
  				todoify(tokens[i], lastId, options, state.Token);
  				lastId += 1;
  				attrSet(tokens[i-2], 'class', options.liClass);
  				attrSet(tokens[parentToken(tokens, i-2)], 'class', options.ulClass);
  			}
  		}
  	});
  };
  
  function attrSet(token, name, value) {
  	var index = token.attrIndex(name);
  	var attr = [name, value];
  
  	if (index < 0) {
  		token.attrPush(attr);
  	} else {
  		token.attrs[index] = attr;
  	}
  }
  
  function parentToken(tokens, index) {
  	var targetLevel = tokens[index].level - 1;
  	for (var i = index - 1; i >= 0; i--) {
  		if (tokens[i].level === targetLevel) {
  			return i;
  		}
  	}
  	return -1;
  }
  
  function isTodoItem(tokens, index) {
  	return isInline(tokens[index]) &&
  	       isParagraph(tokens[index - 1]) &&
  	       isListItem(tokens[index - 2]) &&
  	       startsWithTodoMarkdown(tokens[index]);
  }
  
  function todoify(token, lastId, options, TokenConstructor) {
  	var id;
  	id = options.idPrefix + lastId
  	token.children[0].content = token.children[0].content.slice(3);
  	// label
  	token.children.unshift(beginLabel(id, TokenConstructor));
  	token.children.push(endLabel(TokenConstructor));
  	// checkbox
  	token.children.unshift(makeCheckbox(token, id, options, TokenConstructor));
  	if (options.divWrap) {
  		token.children.unshift(beginWrap(options, TokenConstructor));
  		token.children.push(endWrap(TokenConstructor));
  	}
  }
  
  function makeCheckbox(token, id, options, TokenConstructor) {
  	var checkbox = new TokenConstructor('checkbox_input', 'input', 0);
  	checkbox.attrs = [["type", "checkbox"], ["id", id]];
  	var checked = /^\[[xX]\][ \u00A0]/.test(token.content); // if token.content starts with '[x] ' or '[X] '
  	if (checked === true) {
  	  checkbox.attrs.push(["checked", "true"]);
  	}
  	if (options.disabled === true) {
  	  checkbox.attrs.push(["disabled", "true"]);
  	}
  	
  	return checkbox;
  }
  
  function beginLabel(id, TokenConstructor) {
  	var label = new TokenConstructor('label_open', 'label', 1);
  	label.attrs = [["for", id]];
  	return label;
  }
  
  function endLabel(TokenConstructor) {
  	return new TokenConstructor("label_close", "label", -1);
  }
  
  // these next two functions are kind of hacky; probably should really be a
  // true block-level token with .tag=='label'
  function beginWrap(options, TokenConstructor) {
  	var token = new TokenConstructor('checkbox_open', 'div', 0);
  	token.attrs = [["class", options.divClass]];
  	return token;
  }
  
  function endWrap(TokenConstructor) {
  	var token = new TokenConstructor('checkbox_close', 'div', -1);
  	// token.content = '</label>';
  	return token;
  }
  
  function isInline(token) { return token.type === 'inline'; }
  function isParagraph(token) { return token.type === 'paragraph_open'; }
  function isListItem(token) { return token.type === 'list_item_open'; }
  
  function startsWithTodoMarkdown(token) {
  	// The leading whitespace in a list item (token.content) is already trimmed off by markdown-it.
  	// The regex below checks for '[ ] ' or '[x] ' or '[X] ' at the start of the string token.content,
  	// where the space is either a normal space or a non-breaking space (character 160 = \u00A0).
  	return /^\[[xX \u00A0]\][ \u00A0]/.test(token.content);
  }
  