The macro's can expand to other macro's that expand to other macro's ...:

perl-current $ ./perl -Ilib Porting/expand-macro.pl SvPVX
`sh  cflags "optimize='-O2 -g'" try.c` -E try.c > try.i
          CCCMD =  ccache g++ -DPERL_CORE -c -D_REENTRANT -D_GNU_SOURC
+E -fPIC -DDEBUGGING -DDEBUGGING -fno-strict-aliasing -pipe -fstack-pr
+otector -I/pro/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=
+64  -O2 -g  -Wall -ansi -W -Wextra -Wendif-labels -Wwrite-strings -Wn
+o-unused-variable -Wno-unused-parameter
# 4 "SvPVX expands to"
(*({ SV *const _svpvx = ((SV *)({ void *_p = (A0); _p; })); ((((svtype
+)((_svpvx)->sv_flags & 0xff)) >= SVt_PV) ? static_cast<void> (0) : __
+assert_fail ("((svtype)((_svpvx)->sv_flags & 0xff)) >= SVt_PV", "SvPV
+X expands to", 4, __PRETTY_FUNCTION__)); ((((svtype)((_svpvx)->sv_fla
+gs & 0xff)) != SVt_PVAV) ? static_cast<void> (0) : __assert_fail ("((
+svtype)((_svpvx)->sv_flags & 0xff)) != SVt_PVAV", "SvPVX expands to",
+ 4, __PRETTY_FUNCTION__)); ((((svtype)((_svpvx)->sv_flags & 0xff)) !=
+ SVt_PVHV) ? static_cast<void> (0) : __assert_fail ("((svtype)((_svpv
+x)->sv_flags & 0xff)) != SVt_PVHV", "SvPVX expands to", 4, __PRETTY_F
+UNCTION__)); ((!((((_svpvx)->sv_flags & (0x00004000|0x00008000)) == 0
+x00008000) && (((svtype)((_svpvx)->sv_flags & 0xff)) == SVt_PVGV || (
+(svtype)((_svpvx)->sv_flags & 0xff)) == SVt_PVLV))) ? static_cast<voi
+d> (0) : __assert_fail ("!((((_svpvx)->sv_flags & (0x00004000|0x00008
+000)) == 0x00008000) && (((svtype)((_svpvx)->sv_flags & 0xff)) == SVt
+_PVGV || ((svtype)((_svpvx)->sv_flags & 0xff)) == SVt_PVLV))", "SvPVX
+ expands to", 4, __PRETTY_FUNCTION__)); ((!(((svtype)((_svpvx)->sv_fl
+ags & 0xff)) == SVt_PVIO && !(((XPVIO*) (_svpvx)->sv_any)->xio_flags 
+& 64))) ? static_cast<void> (0) : __assert_fail ("!(((svtype)((_svpvx
+)->sv_flags & 0xff)) == SVt_PVIO && !(((XPVIO*) (_svpvx)->sv_any)->xi
+o_flags & 64))", "SvPVX expands to", 4, __PRETTY_FUNCTION__)); &((_sv
+pvx)->sv_u.svu_pv); }))
[download]

Sometimes that helps but sometimes it just obfuscates more then it explains