Atomic Group

C:\msys64\usr\bin>cat animals.txt
the big dog
the small bird
the biggest dog
the small cat

C:\msys64\usr\bin>grep -P --color "(?>big|biggest)" animals.txt
the big dog
the biggest dog

C:\msys64\usr\bin>grep -P --color "(?>biggest|big)" animals.txt
the big dog
the biggest dog

C:\msys64\usr\bin>cat abc.txt
abc
abcc

C:\msys64\usr\bin>grep -P --color "a(?>b|bc)c" abc.txt
abc
abcc

C:\msys64\usr\bin>grep -P --color "a(?>bc|b)c" abc.txt
abcc

C:\msys64\usr\bin>cat num.txt
Dat foo 13.45 and $600 bar {baz:70} and {8}

C:\msys64\usr\bin>grep -P --color "(?<!{)([0-9]+(\.[0-9]+)?)(?!})" num.txt
Dat foo 13.45 and $600 bar {baz:70} and {8}

C:\msys64\usr\bin>grep -P --color "(?<!{)(?>[0-9]+(\.[0-9]+)?)(?!})" num.txt
Dat foo 13.45 and $600 bar {baz:70} and {8}