write support chapter

[Mouvedia]

properties

@support (property) { }

!

!@support (banana) { }
@support (!banana & orange) { }

tickets

@support (!fixed[354]) { }

version

@support (version ≥ 1.2) { }

filters

@support (filter[""]) { }

combinators

@support (combinator[""]) { }

modifiers

@support (modifier[""]) { }

objects

@support (object[""]) { }

arguments and values

name
PRO: flexibility
CON: complexity

position
PRO: reliability
CON: usability

[Mouvedia]

After much discussion it seems we have to use an instruction instead.

#support (property) { }
#support (354) { }
#support (≥ v1.2) { }
#support (@object) { }
#support (:filter) { }
#support (::flag) { }
#support (/splitter) { }

I must add that #support (property) will resolve to #support (@container.property) by default to avoid property collusions.

#support (@text.direction)
//is not equivalent to
#support (@container.direction)

Concerning modifiers and combinators, what's really important is if they are supported or not: whether they are a combinator or a modifier is not relevant (since we would never introduce one which could be at the same time a combinator or a modifier).
So we can do this safely:

//checks if the + combinator is supported
#support (+) { }
//checks if the $ modifier is supported
#support ($) { }

emended : to reflect veo's comment

[veosotano]

we should always put the @ in front of an object type, so it would actually be more like

#support (@text.direction)

[Mouvedia]

#support (justify of contentAlignX) { }

We can't use the index for properties with one value. And the values of the properties which accept multiple values aren't ordered so it wouldn't make sense to use #support on one: you just globally check if the property's value is supported or not. Hence using the index is out of the window.

 //checks if this object is supported for all values of this property
 #support (@hsb of border) { }

[Mouvedia]

#70