Inconsistent documentation of -source argument to create_generated_clock.

[Wren6991]

The API listing for create_generated_clock says -source is a pin:

The examples show it being used with a clock instead (which is what I'm more used to from other tools):

Which is correct? Experimentally, passing a clock seems to raise an error saying the clock is not a pin.

# Primary input clock. Source of all other clocks except for DCK.
create_clock [get_pins i_chip_core.clocks_u.clkroot_padin_clk_u.magic_clkroot_anchor_u/Z] \
    -name padin_clk \
    -period $PADIN_CLK_PERIOD

create_generated_clock [get_pins i_chip_core.clocks_u.clkroot_sys_u.magic_clkroot_anchor_u/Z] \
    -name clk_sys \
    -source padin_clk \
    -divide_by 2

results in:

Error: chip_top.sdc line 46, pin padin_clk not found.