   It raises `BadMapError` if the first element is not a map.
 
   Allowed in guard tests. Inlined by the compiler.
+
+  ## Examples
+
+      iex> is_map_key(%{a: "foo", b: "bar"}, :a)
+      true
+
+      iex> is_map_key(%{a: "foo", b: "bar"}, :c)
+      false
   """
   @doc guard: true, since: "1.10.0"
   @spec is_map_key(map, term) :: boolean

  Giving it an empty list raises:

      tl([])
      #=> ** (ArgumentError) argument error

  """
  @doc guard: true

  Giving it an empty list raises:

      hd([])
      ** (ArgumentError) argument error

  """
  @doc guard: true
