[css-flexbox-1] Clarify min-content and max-content sizing on the block axis

[gitspeaks]

The spec doesn’t clearly explain how the min-content keyword affect the block size of flex containers. The behavior differs from max-content (see #6457 (comment)), but this isn’t intuitive (see #6457 (comment)), and no browser seems to follow the spec (see #12103 (comment)).

Also, section 9.9.3 lacks definitions for a flex item's cross-size min/max-content contributions.

Please clarify these points in the spec.

[Loirooriol]

It's defined in https://drafts.csswg.org/css-flexbox-1/#intrinsic-sizes, it should work for both axes.

Anyways, the algorithm is not web compatible and needs to be changed: #8884 (comment)

[gitspeaks]

It's defined in https://drafts.csswg.org/css-flexbox-1/#intrinsic-sizes, it should work for both axes.

1. When the block-size is in the cross direction: Section 9.9.2. Flex Container Intrinsic Cross Sizes applies. However, this section does not distinguish between min-content and max-content sizes, contrary to what the comments in my initial message suggest.

2. When the block-size is in the main direction: Section 9.9.1. Flex Container Intrinsic Main Sizes applies. Specifically, the "ideal algorithm" notes:

   "The min-content main size of a single-line flex container is calculated identically to the max-content main size, except that the flex items’ min-content contributions are used instead of their max-content contributions."

However, it's unclear what the actual difference is—if any—between the max-content and min-content contributions of a flex item when block-size is involved.

3. Section 9.9.3. Flex Item Intrinsic Size Contributions explicitly refers only to the main size. When the inline size is the main direction and block size is the cross direction, it’s unclear how this section applies to block-size. If the instructions are indeed meant to apply to both axes, then using “main size” is misleading, and the spec should explicitly state that the logic applies to both dimensions.