[css3-flexbox] question about calculating "hypothetical main size"

I am having trouble understanding the algorithm here, and I'll
appreciate some help, for example, a pointer to a previous discussion.


9.2. Line Length Determination

  # 3. Determine the flex base size and hypothetical main size of each
  # item:
  #
  # ...
  #    Otherwise, if the flex container's main-axis is parallel to the
  # item's inline-axis, lay out the item using the available space and
  # its flex basis if the item is inflexible,

Question 1: What does use the available space *and* its flex basis mean?
Using its flex basis as the available space? Using the maximum of
available space from the flex container and the flex basis?

Question 2: What is the flex base size of

<div style="display: flex; width: fit-content"><!--floated container-->
  <div style="flex: 0 0 50%;">
  </div>
</div>

The flex item is inflexible and the percentage is resolved against an
flex container with indefinite width and hence indefinite by definition.
How do you resolve 50% at this point?

I wonder if I am misunderstanding the definition of "definite size"...

  # or ‘auto’ otherwise, treating ‘auto’ as ‘max-content’...
  # If the flex basis is ‘fill-available’, or ‘fit-content’, and
  # the flex container is being sized under a min-content or
  # max-content main-size constraint, size the item under that
  # constraint instead. The flex base size is the item's resulting
  # measure.

Question 3: What does "sized under a min-content or max-content
main-size constraint" mean? What are the examples besides "width:
min-content" and "width: max-content" on the flex container?

Is this partially duplicating

  # The hypothetical main size is the item's flex bease size clamped
  # according to its min and max main size properties.

?


Cheers,
Kenny