code: function travels(subsetMap) {
                              var newSubsetMap = {};
                              Object.keys(subsetMap).forEach(function (i) {
                                  var index = +i;
                                  parsedGlyfMap[index] = true;
                                  // 当前的和下一个一样，或者最后一个无轮廓
                                  if (loca[index] === loca[index + 1]) {
                                      glyphs[index] = {
                                          contours: []
                                      };
                                  }
                                  else {
                                      glyphs[index] = parse(reader, ttf, startOffset + loca[index]);
                                  }
  
                                  if (glyphs[index].compound) {
                                      glyphs[index].glyfs.forEach(function (g) {
                                          if (!parsedGlyfMap[g.glyphIndex]) {
                                              newSubsetMap[g.glyphIndex] = true;
                                          }
                                      });
                                  }
                              });
  
                              if (!lang.isEmptyObject(newSubsetMap)) {
                                  travels(newSubsetMap);
                              }
                          }
docs: 循环解析subset相关的glyf，包括复合字形相关的字形