[css-align] in which cases does 'left'/'right' compute to 'start' exactly?

In the description of 'left' (and 'right'), the spec says:
"If the property's axis is not parallel with the inline axis,
this value computes to 'start'."
https://drafts.csswg.org/css-align-3/#positional-values

Does this include values where those keywords are combined
with other keywords?  I.e. does the computed value for
"align-content: left safe" become "start safe" ?
"align-content: stretch left" become "stretch start" ?
"align-content: stretch left safe" become "stretch start safe" ?
etc. or does that sentence just apply when the specified
value is exactly "left" ?

Also, I want to double-check I understand the first part of
the sentence correctly: this means that 'left' always becomes
'start' for all 'align-*' properties, and always computes to
itself for all 'justify-*' properties, right?

(I would appreciate a quick answer as I am writing code to
implement this in Gecko right now.)

Thanks,
Mats