code: function fileAppendIdPart(file, part, extensions) {                      // 237
      // Always append relative to a directory.                              // 238
      while (file && ! fileIsDirectory(file)) {                              // 239
        file = file.p;                                                       // 240
      }                                                                      // 241
                                                                             // 242
      if (! file || ! part || part === ".") {                                // 243
        return file;                                                         // 244
      }                                                                      // 245
                                                                             // 246
      if (part === "..") {                                                   // 247
        return file.p;                                                       // 248
      }                                                                      // 249
                                                                             // 250
      var exactChild = getOwn(file.c, part);                                 // 251
                                                                             // 252
      // Only consider multiple file extensions if this part is the last     // 253
      // part of a module identifier and not equal to `.` or `..`, and there
      // was no exact match or the exact match was a directory.              // 255
      if (extensions && (! exactChild || fileIsDirectory(exactChild))) {     // 256
        for (var e = 0; e < extensions.length; ++e) {                        // 257
          var child = getOwn(file.c, part + extensions[e]);                  // 258
          if (child) {                                                       // 259
            return child;                                                    // 260
          }                                                                  // 261
        }                                                                    // 262
      }                                                                      // 263
                                                                             // 264
      return exactChild;                                                     // 265
    }
docs: 235 236