Search notes:

Microsoft.PowerShell.Commands.Internal.Format (namespace)

PS C:\> $ft = (get-psReadLineKeyHandler | format-table)
PS C:\> $ft[0 .. 2] | foreach-object {$_.GetType().FullName}

Microsoft.PowerShell.Commands.Internal.Format.FormatStartData
Microsoft.PowerShell.Commands.Internal.Format.GroupStartData
Microsoft.PowerShell.Commands.Internal.Format.FormatEntryData

Index