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Precise syntax of CSS3 colors

Precise syntax of CSS3 colors

Problem

I couldn't find a precise definition of legal syntax for CSS3 colors, either as regular expression, BNF or whatever strict formal definition there might be. Some info can be derived from the verbal description in the CSS3 Color Module (for example that comma separated lists may contain whitespace), but I don't see whether e.g. leading zeros in something like

rgb(010,005,255)
rgba(050%,1%,01%,0)

are actually legal, or omitting leading zeros of decimal fractions, like

rgba(100,100,100,.5)

I'm not talking about what is tolerated by browsers, I'm asking whether this is officially legal CSS3 syntax as I'm interested in the use of these color definitions in non-browser applications as well.

Problem courtesy of: Thomas W

Solution

As you found already, the CSS3 Color Module specification says

The format of an RGB value in the functional notation is 'rgb(' followed by a comma-separated list of three numerical values (either three integer values or three percentage values) followed by ')'

But you then need to look in basic data types section of CSS 2.1 to find out what an integer or a percentage value is and it says...

Some value types may have integer values (denoted by ) or real number values (denoted by ). Real numbers and integers are specified in decimal notation only. An consists of one or more digits "0" to "9". A can either be an , or it can be zero or more digits followed by a dot (.) followed by one or more digits. Both integers and real numbers may be preceded by a "-" or "+" to indicate the sign. -0 is equivalent to 0 and is not a negative number.

So integers and numbers can have leading zeros.

Then later on basic data types says

The format of a percentage value (denoted by in this specification) is a immediately followed by '%'.

So percentages can have leading zeros too.

Solution courtesy of: Robert Longson

Discussion

View additional discussion.



This post first appeared on CSS3 Recipes - The Solution To All Your Style Problems, please read the originial post: here

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Precise syntax of CSS3 colors

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