[css-logical] Add block-start and block-end values to caption-side property

[ramiy]

While documenting the caption-side property on MDN we noticed that the flow-relative block-start and block-end values are not defined by any spec, although they are mentioned in the spec.

• Cascading Style Sheets Level 2 Revision 2 spec defines the top | bottom | inherit values.
• CSS Logical Properties and Values Level 1 spec defines the inline-start | inline-end values.

The block-start and block-end values are mentioned but not really defined in the spec.

[SebastianZ]

Logical Properties 1 says this:

The existing top and bottom values are idiosyncratically redefined as assigning to the block-start and block-end sides of the table, respectively.

So those actually are flow-relative, even when they refer to physical sides.

Though I think it makes sense to add them as aliases to the existing top and bottom keywords. Therefore, I have created #9623 to discuss their addition.

Sebastian

[Loirooriol]

This needs to be discussed in #9623

But anyways, if we end up adding block-star and block-end, it doesn't make sense to condition them on supporting left and right.

[ramiy]

Cascading Style Sheets (CSS) Level 2 - defines only top | bottom | inherit

CSS Logical Properties and Values Level 1 - defines only inline-start | inline-end

No spec defines block-start and block-end.