code: function extractParts (str, indexA, indexB) {
  	let part = str.substr(indexA, indexB);
  
  	part = part.replace(/</g, '&lt;').replace(/>/g, '&gt;');
  	part = part.replace(/\n/g, '<span class="invisible"> \u21A9</span>\n');
  	part = part.replace(/\t/g, '<span class="invisible tab">\u2192</span>');
  	return part;
  }
docs: Get part of string and replace special symbols there
  @param {string} str
  @param {number} indexA
  @param {number} [indexB]
  @returns {string}
  @private
  @sourceCode