requested_variants='+universal' for port with no +universal variant?

[Jim DeLaHunt]

Hello, folks:

I am working through the Migration[1] procedure after upgrading my macOS 
version. I made a list of my installed ports using `port -qv installed`. 
Curiously, a number of the ports in that list include the notation 
`requested_variants='+universal'`, even though the port appears to have 
no +universal variant. For example,

bison @3.7.6_1+universal requested_variants='+universal' 
platform='darwin 17' archs='x86_64' date='2021-07-04T14:08:44-0700'
bison @3.7.6_2+universal (active) requested_variants='+universal' 
platform='darwin 17' archs='x86_64' date='2021-08-12T18:44:11-0700'

But there appars to be no +universal variant:

% port info bison
bison @3.7.6_2 (devel)
Sub-ports:            bison-runtime

Description:          Bison is a general-purpose parser generator that 
converts an annotated context-free grammar into a deterministic LR
                       or generalized LR (GLR) parser employing LALR(1) 
parser tables. As an experimental feature, Bison can also generate
                       IELR(1) or canonical LR(1) parser tables. Once 
you are proficient with Bison, you can use it to develop a wide range
                       of language parsers, from those used in simple 
desk calculators to complex programming languages.
Homepage:             https://www.gnu.org/software/bison

Extract Dependencies: xz
Library Dependencies: gettext, libiconv, m4
Runtime Dependencies: bison-runtime
Platforms:            darwin
License:              (GPL-3+ or Permissive)
Maintainers:          none
% port info --variants bison
variants:

Perhaps these +universal request are a relic of the distant past? I have 
migrated this MacPorts installation forward through several OS versions 
and multiple computers. It might be that some data originated on a 
PowerPC mac long ago, when +universal was significant.

I have on MacPorts 2.7.1 and macOS 10.14 Mojave (just upgrade from 10.13 
High Sierra) and a 7-year-old Mac with an intel CPU.

The buildUniversal wiki page[2] seems to be 8 years old and not relevant 
to my situation.

Q1. What does a `+universal` variant request do, on MacPorts 2.7.1 and 
macOS 10.14 Mojave and a Mac with an intel CPU, if the port does not 
advertise a `+universal` variant?

Q2. Is there a `+universal` variant which is built in to MacPorts, even 
if the port does not advertise a `+universal` variant? MacPorts Guide, 
5. Portfile Reference, 5.5.1. User-Selected Variants[3] seems to imply 
"yes".

Q3. Are there ports which have a `+universal` variant which is important 
for my system? How do I find this out, and understand the significance?

Q4. Should I edit my list of installed ports to remove the `+universal` 
from the port identifier and requested_variants keyword? For instance, 
should I change the bison entry from:

bison @3.7.6_1+universal requested_variants='+universal' 
platform='darwin 17' archs='x86_64' date='2021-07-04T14:08:44-0700'
bison @3.7.6_2+universal (active) requested_variants='+universal' 
platform='darwin 17' archs='x86_64' date='2021-08-12T18:44:11-0700'

into:

bison @3.7.6_1 requested_variants='' platform='darwin 17' archs='x86_64' 
date='2021-07-04T14:08:44-0700'
bison @3.7.6_2 (active) requested_variants='' platform='darwin 17' 
archs='x86_64' date='2021-08-12T18:44:11-0700'

Note: this list of installed ports had some entries with `archs='i386 
x86_64'`. I already got rid of the `i386` arch entry.

[1] https://trac.macports.org/wiki/Migration
[2] https://trac.macports.org/wiki/howto/buildUniversal
[3] https://guide.macports.org/chunked/reference.variants.html

Thank you in advance for your help.
      —Jim DeLaHunt