class_docstr: Create a FeatureCollection.
  
  Parameters
  ----------
  feature_descriptors : Union[FeatureDescriptor, MultipleFeatureDescriptors, FeatureCollection, List[Union[FeatureDescriptor, MultipleFeatureDescriptors, FeatureCollection]]], optional
      Initial (list of) feature(s) to add to collection, by default None
  
  Notes
  -----
  * The `series_name` property of the `FeatureDescriptor`s should **not withhold a "|"
    character**, since "|" is used to join the series names of features which use
    multiple series as input).<br>
    e.g.<br>
      * `ACC|x` is **not** allowed as series name, as this is ambiguous and could
        represent that this feature is constructed with a combination of the `ACC`
        and `x` signal.<br>
        Note that `max|feat` is allowed as feature output name.
  * Both the `series_name` and `output_name` property of the `FeatureDescriptor`s
    **should not withhold "__"** in its string representations. This constraint is
    mainly made for readability purposes.
  
  The two statements above will be asserted
code: def _get_stroll_feat_length(self) -> int:
      return sum(
          len(self._feature_desc_dict[k])
          for k in self._feature_desc_dict.keys()
      )
  
imports: from __future__ import annotations
  import warnings
  import os
  import traceback
  import uuid
  from copy import deepcopy
  from pathlib import Path
  from typing import Any, Callable, Dict, Iterable, List, Optional, Tuple, Union
  import dill
  import numpy
  import pandas
  from multiprocess import Pool
  from tqdm.auto import tqdm
  from ..features.function_wrapper import FuncWrapper
  from ..utils.attribute_parsing import AttributeParser
  from ..utils.data import flatten, to_list, to_series_list
  from ..utils.logging import add_logging_handler, delete_logging_handlers
  from ..utils.time import parse_time_arg, timedelta_to_str
  from .feature import FeatureDescriptor, MultipleFeatureDescriptors
  from .logger import logger
  from .segmenter import StridedRolling, StridedRollingFactory
  from .utils import _check_start_end_array, _determine_bounds
label_desc: Use image node_id 11 for calling the FeatureCollection obj's underlying member method code with example usage: obj._get_stroll_feat_length() and returns: sum