docstr: Get the helptext string for a single trait.
  
  :param inst:
      If given, its current trait values will be used in place of
      the class default.
  :param helptext:
      If not given, uses the `help` attribute of the current trait.
code: def class_get_trait_help(
      cls,
      trait: TraitType[t.Any, t.Any],
      inst: HasTraits | None = None,
      helptext: str | None = None,
  ) -> str:
      """Get the helptext string for a single trait.
  
      :param inst:
          If given, its current trait values will be used in place of
          the class default.
      :param helptext:
          If not given, uses the `help` attribute of the current trait.
      """
      assert inst is None or isinstance(inst, cls)
      lines = []
      header = f"--{cls.__name__}.{trait.name}"
      if isinstance(trait, (Container, Dict)):
          multiplicity = trait.metadata.get("multiplicity", "append")
          if isinstance(trait, Dict):
              sample_value = "<key-1>=<value-1>"
          else:
              sample_value = (
                  "<%s-item-1>" % trait.__class__.__name__.lower()
              )
          if multiplicity == "append":
              header = f"{header}={sample_value}..."
          else:
              header = f"{header} {sample_value}..."
      else:
          header = f"{header}=<{trait.__class__.__name__}>"
      # header = "--%s.%s=<%s>" % (cls.__name__, trait.name, trait.__class__.__name__)
      lines.append(header)
  
      if helptext is None:
          helptext = trait.help
      if helptext != "":
          helptext = "\n".join(wrap_paragraphs(helptext, 76))
          lines.append(indent(helptext))
  
      if "Enum" in trait.__class__.__name__:
          # include Enum choices
          lines.append(indent("Choices: %s" % trait.info()))
  
      if inst is not None:
          lines.append(
              indent(f"Current: {getattr(inst, trait.name or '')!r}")
          )
      else:
          try:
              dvr = trait.default_value_repr()
          except Exception:
              dvr = None  # ignore defaults we can't construct
          if dvr is not None:
              if len(dvr) > 64:
                  dvr = dvr[:61] + "..."
              lines.append(indent("Default: %s" % dvr))
  
      return "\n".join(lines)
  
imports: from __future__ import annotations
  import logging
  import typing
  from copy import deepcopy
  from textwrap import dedent
  from traitlets.traitlets import Any, Container, Dict, HasTraits, Instance, TraitType, default, observe, observe_compat, validate
  from traitlets.utils import warnings
  from traitlets.utils.bunch import Bunch
  from traitlets.utils.text import indent, wrap_paragraphs
  from .loader import Config, DeferredConfig, LazyConfigValue, _is_section_key
label_desc: Use image node_id 8 for calling the Configurable obj's underlying member method code with example usage: obj.class_get_trait_help(cls, trait, inst, helptext) and returns: str