code: function splitTickText(d, maxWidth) {
                      var tickText = textFormatted(d),
                          subtext, spaceIndex, textWidth, splitted = [];
  
                      if (Object.prototype.toString.call(tickText) === "[object Array]") {
                          return tickText;
                      }
  
                      if (!maxWidth || maxWidth <= 0) {
                          maxWidth = isVertical ? 95 : params.isCategory ? (Math.ceil(scale1(ticks[1]) - scale1(ticks[0])) - 12) : 110;
                      }
  
                      function split(splitted, text) {
                          spaceIndex = undefined;
                          for (var i = 1; i < text.length; i++) {
                              if (text.charAt(i) === ' ') {
                                  spaceIndex = i;
                              }
                              subtext = text.substr(0, i + 1);
                              textWidth = sizeFor1Char.w * subtext.length;
                              // if text width gets over tick width, split by space index or crrent index
                              if (maxWidth < textWidth) {
                                  return split(
                                      splitted.concat(text.substr(0, spaceIndex ? spaceIndex : i)),
                                      text.slice(spaceIndex ? spaceIndex + 1 : i)
                                  );
                              }
                          }
                          return splitted.concat(text);
                      }
  
                      return split(splitted, tickText + "");
                  }
docs: this should be called only when category axis