why forbidding "include" a sub-makefile.am with absolute path

[赵峰(远猷)]

Hi guys,
I find the following code in automake.
>my $PATH_PATTERN = '(\w|[+/.-])+';
># This will pass through anything not of the prescribed form.
>my $INCLUDE_PATTERN = ('^include\s+'
>                       . '((\$\(top_srcdir\)/' . $PATH_PATTERN . ')'
>                       . '|(\$\(srcdir\)/' . $PATH_PATTERN . ')'
>                       . '|([^/\$]' . $PATH_PATTERN . '))\s*(#.*)?' . "\$");

but why need forbidding "include" sub-makefile.ams with absolute path by the 
last line?
In my Makefile.am, i need to include another sub-makefile from the path in a 
variable(ANOTHER_PJ_DIR) declared with AC_SUBET> Makefile.am
> include @another_pj_...@common.mk
the ANOTHER_PJ_DIR contains an absolute path of another project, but the 
include does't parsed by automake.How can i do it?thx!
miles.zhaof

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