pattern is "ms=e+1".  "ms" stands for Match Start.
This defines an offset for the start of the match.  Normally the match starts
where the pattern matches.  "e+1" means that the match now starts at the end
of the pattern match, and then one character further.
   The offset for the end pattern is "me=s-1".  "me" stands for Match End.
"s-1" means the start of the pattern match and then one character back.  The
result is that in this text:

	if (foo == bar) ~

Only the text "foo == bar" will be highlighted as xCond.

More about offsets here: |:syn-pattern-offset|.


ONELINE

The "oneline" argument indicates that the region does not cross a line
boundary.  For example: >

	:syntax region xIfThen start=/if/ end=/then/ oneline

This defines a region that starts at "if" and ends at "then".  But if there is
no "then" after the "if", the region doesn't match.

	Note:
	When using "oneline" the region doesn't start if the end pattern
	doesn't match in the same line.  Without "oneline" Vim does _not_
	check if there is a match for the end pattern.  The region starts even
	when the end pattern doesn't match in the rest of the file.


CONTINUATION LINES AND AVOIDING THEM

Things now become a little more complex.  Let's define a preprocessor line.
This starts with a # in the first column and continues until the end of the
line.  A line that ends with \ makes the next line a continuation line.  The
way you handle this is to allow the syntax item to contain a continuation
pattern: >

	:syntax region xPreProc start=/^#/ end=/$/ contains=xLineContinue
	:syntax match xLineContinue "\\$" contained

In this case, although xPreProc normally matches a single line, the group
contained in it (namely xLineContinue) lets it go on for more than one line.
For example, it would match both of these lines:

	#define SPAM  spam spam spam \ ~
			bacon and spam ~

In this case, this is what you want.  If it is not what you want, you can call
for the region to be on a single line by adding "excludenl" to the contained
pattern.  For example, you want to highlight "end" in xPreProc, but only at
the end of the line.  To avoid making the xPreProc continue on the next line,
like xLineContinue does, use "excludenl" like this: >

	:syntax region xPreProc start=/^#/ end=/$/
		\ contains=xLineContinue,xPreProcEnd
	:syntax match xPreProcEnd excludenl /end$/ contained
	:syntax match xLineContinue "\\$" contained

"excludenl" must be placed before the pattern.  Since "xLineContinue" doesn't
have "excludenl", a match with it will extend xPreProc to the next line as
before.

==============================================================================
*44.8*	Clusters

One of the things you will notice as you start to write a syntax file is that
you wind up generating a lot of syntax groups.  Vim enables you to define a
collection of syntax groups called a cluster.
   Suppose you have a language that contains for loops, if statements, while
loops, and functions.  Each of them contains the same syntax elements: numbers
and identifiers.  You define them like this: >

	:syntax match xFor /^for.*/ contains=xNumber,xIdent
	:syntax match xIf /^if.*/ contains=xNumber,xIdent
	:syntax match xWhile /^while.*/ contains=xNumber,xIdent

You have to repeat the same "contains=" every time.  If you want to add
another contained item, you have to add it three times.  Syntax clusters
simplify these definitions by enabling you to have one cluster stand for
several syntax groups.
   To define a cluster for the two items that the three groups contain, use
the following command: >

	:syntax cluster xState contains=xNumber,xIdent

Clusters are used inside other syntax items just like any syntax group.
Their names start with @.  Thus, you can define the three groups like this: >

	:syntax match xFor /^for.*/ contains=@xState
	:syntax match xIf /^if.*/ contains=@xState
	:syntax match xWhile /^while.*/ contains=@xState

You can add new group names to this cluster with the "add" argument: >

	:syntax cluster