STM32 Arduino framework: board_build.core options are unclear

See: https://docs.platformio.org/en/latest/platforms/ststm32.html#switching-between-arduino-cores

Switching between Arduino cores

There are three different Arduino cores for STM32 microcontrollers: STM32Duino, Arduino STM32 (maple) and STM32L0. All of them have been developed independently, therefore, have different functionality and set of internal libraries. By default, official STM32Duino core is used (except cases when a board supports only one specific core). Some of the boards support all three cores. To change the core you can use a board_build.core option that needs be added to build_flags:

An example of “platformio.ini” (Project Configuration File) with maple core

[env:hy_tinystm103tb]
platform = ststm32
framework = arduino
board = hy_tinystm103tb
board_build.core = maple

Only 'maple' is given as example.
What are the exact values (and correct casing) for the other two options?

The documentation should be more clear about this and show a table listing the different possible values.

Open the STM32 Arduino cores section at the linked ststm32 platform documentation page and verify the exact values and casing for each supported core. Update that section with a table listing all possible values, including the existing maple example; the documentation is done when the options and their casing are unambiguous.