pattern rule with multiple patterns for targets and double colon

[baumann@pan]

I have some questions on the post
http://groups.google.com/group/gnu.utils.help/browse_thread/thread/c73e3e9d136a8fa2/80b2c1f60ea8120e?lnk=gst&q=Makefile+Multiple+Targets+in+a+Rule+&rnum=8#
1.
[quote]
Paul D. Smith
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         More options Mar 4 1998, 4:00 pm
Newsgroups: gnu.utils.help
From: psm...@baynetworks.com (Paul D. Smith)
Date: 1998/03/04
Subject: Re: Make - mulitple targets but from lists
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%% John Hetherington <j...@eagpde.co.uk> writes:

  jh> # Can anyone help me ?
  jh> #
  jh> # I need this makefile to generate the following output,
  jh> #
  jh> #  Created r.x.c from x.c
  jh> #  Created s.x.c from x.c
  jh> #  Created t.x.c from x.c
  jh> #  Created r.y.c from y.c
  jh> #  Created s.y.c from y.c
  jh> #  Created t.y.c from y.c
  jh> #
  jh> # but only using the contents of the two lists, SRCS and
PREFIXES.

  jh> SRCS = x.c y.c
  jh> PREFIXES = r s t

I don't see any excellent way to do it.  However, here are two
alternatives:

The first uses pattern rules.  However, remember that a pattern rule
with multiple patterns for targets means that a single invocation of
this rule builds all the targets; that's not actually what you want
but
there's no way to avoid it, so you'll have to really do that:
[/quote]
I dont understand
"However, remember that a pattern rule
with multiple patterns for targets means that a single invocation of
this rule builds all the targets"

I could not find the same statement in the Make Manual.

it's better if there are more explaintations and more examples.

2.
[quote]
  .SUFFIXES:

  SRCS = x.c y.c
  PREFIXES = r s t

  PATTERN = $(foreach p,$(PREFIXES),$(p).%)

  ALL = $(foreach p,$(PREFIXES),$(foreach s,$(SRCS),$(p).$(s)))

  all: $(ALL)

  $(PATTERN):: %
          @for p in $(PREFIXES); do \
            echo Created $$p.$< from $<; \
          done

Here we use a shell loop in the pattern rule to run the command once
per
prefix.
[/quote]
I could understand why double colon needed here.


anyone could resolve my questions?
TIA
B@P