what does the number mean that prefix package name?

Question

I want get the dependency pkg names of some pkg with repoquery, like this:

[root@localhost home]#  repoquery  --requires --resolve  --envra    httpd
0:pcre-8.32-15.el7_2.1.x86_64
0:apr-util-1.5.2-6.el7.x86_64
0:bash-4.2.46-19.el7.x86_64
0:libselinux-2.2.2-6.el7.x86_64
0:systemd-libs-219-19.el7.x86_64
0:mailcap-2.1.41-2.el7.noarch
0:apr-1.4.8-3.el7.x86_64
0:libdb-5.3.21-19.el7.x86_64
0:zlib-1.2.7-15.el7.x86_64
0:lua-5.1.4-14.el7.x86_64
0:systemd-219-19.el7_2.13.x86_64
2:shadow-utils-4.1.5.1-18.el7.x86_64
0:expat-2.1.0-8.el7.x86_64
0:glibc-2.17-106.el7_2.8.x86_64
0:httpd-tools-2.4.6-40.el7.centos.4.x86_64
0:glibc-2.17-105.el7.i686
0:centos-logos-70.0.6-3.el7.centos.noarch

I noticed there is a number and colon before pkg name each line, and I want to know what does the number mean. I have googled, but cannot find any clue.

Answer 1

From "man repoquery":

  Specifying package names
         A package can be referred to in all queries with any of the following:

         name
         name.arch
         name-ver
         name-ver-rel
         name-ver-rel.arch
         name-epoch:ver-rel.arch
         epoch:name-ver-rel.arch

So, this number is just the epoch.