Documentation: unclear what a "CSS length unit" is

[daattali]

Reading the documentation for layout_columns(), this is the explanation of the gap argument:

A CSS length unit defining the gap (i.e., spacing) between elements provided to .... This argument is only applicable when fillable = TRUE

Clicking on the "CSS length unit" link does not clear up confusion about what sort of values are accepted to this argument. It helps sort of give a rough idea, but it's definitely not clear.

[gadenbuie]

Could you clarify the nature of the confusion? Those docs do list out anticipated values

Single element character vectors must be "auto", "fit-content" or "inherit", a number, or a length calculated by the "calc" CSS function. If the number has a suffix, it must be valid: px, ⁠\%⁠, ch, em, rem, pt, ⁠in⁠, cm, mm, ex, pc, vh, vw, vmin, or vmax. If the number has no suffix, the suffix "px" is appended.

I do think that it'd be slightly better and more precise for the link to say "A CSS length" instead of CSS length unit, since we're expecting both the distance value and its unit. Also, the article on MDN is a good resource we could link to.

[daattali]

This is an "issue" I've had with many shiny functions for a long time, I just figured since the documentation is actively being created in this package, maybe it would get addressed :)

I clicked on the link expecting to be told exactly what a CSS unit. Instead, I was brought to the help page of another function. After reading the details section, it raises more questions: can I use NULL/NA? What do those values mean in this context? Since it's explicitly talking about the case of a single-element vector, does that mean that my argument alos accepts multi-element vectors? Does my CSS unit have to be propertly formatted, or does it run through this validation function and will be "fixed" automatically?

Since there are many places in both shiny and bslib that use the concept of a CSS length unit, perhaps it would be helpful to have a dedicated section just explaining clearly what syntax is expected for a CSS length, instead of linking to a validation function that is very closely related but requires a bit more mental work.

Please close the issue if you disagree :)