[css-speech] Discrepancy between syntax and prose regarding negative frequencies in `voice-*`

[cdoublev]

For voice-pitch and voice-range, the prose allow negative values but not the syntax since 3baba27.

Name: voice-pitch
Value: <frequency [0Hz,∞]> && absolute | [ [ x-low | low | medium | high | x-high ] || [ <frequency [0Hz,∞]> | <semitones> | <percentage> ] ]

<frequency [0Hz,∞]>

A value in frequency units (Hertz or kiloHertz, e.g. 100Hz, +2kHz). Values are restricted to positive numbers when the absolute keyword is specified. Otherwise (when the absolute keyword is not specified), a negative value represents a decrement, and a positive value represents an increment, relative to the inherited value. [...]

Which one is correct?

Cc @SebastianZ