[MacPorts] #15625: Guide doesn't explain variants very well

[MacPorts]

#15625: Guide doesn't explain variants very well
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 Reporter:  myrrhlin at gmail.com       |       Owner:  markd at macports.org
     Type:  defect                   |      Status:  new               
 Priority:  Normal                   |   Milestone:                    
Component:  guide                    |     Version:  1.6.0             
 Keywords:  doc variants guide wiki  |  
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 There are some obvious questions about variants which are not answered in
 the guide (and also not in the FAQ).  I only began to figure out the
 answers by trying things and finding out what worked and what didn't.  The
 guide should be expanded to answer these questions.

  * Can multiple variant options be selected at install time?  (yes)
  * Do variant options sometimes conflict, and how would I know? (??)
  * Can two variants be installed at the same time? (yes, but only one can
 be active at a given time.  use port deactivate on the first variant, then
 install the second)
  * Can an existing variant be modified to add or remove variant options?
 (no)
  * What if I need to add a new option to a variant (or remove one)?
 (uninstall it, then reinstall with the desired options)
  * Is the 'universal' variant considered to be exclusive of all other
 options?  That is, if there is an option that enables liba52 support, am I
 to assume the universal install doesn't have this support?  (??)
  * The documentation mentions turning off 'default' variant options with
 the minus sign syntax -- how do I find out which are the default ones, if
 any (other than reading the portfile)?  (??)

 I might add that the short descriptions of the variants are quite unclear
 to me, and insufficient.  They're the sort of description which are
 adequate if you already know what the options mean.  If you don't, it
 doesn't help much in making wise choices.  I hope you consider support for
 greater documentation of these choices in the portfiles or elsewhere, more
 than a fraction of a line.  The wiki would also be a great place for
 further documentation of this kind, if it was expanded to include pages
 for every port with variants.  Please make it easier somehow for the
 documentation of variants to be expanded.

 Here's an example.  Whats the difference between darwin7, darwin8, macosx
 options as opposed to universal?  I know 10.4 is darwin 8 (you should
 explain that too), but just when do I need to specify that?  Anytime I see
 it given as a variant?  Are darwin7 and darwin8 exclusive?  Are darwin8
 and macosx exclusive?  How would I know?

 Another example.  I see that ffmpeg includes native support for vorbis and
 xvid, but there are variant options to use external libraries instead.
 What are the advantages to each choice?  Which provides greater
 speed/flexibility/etc?

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Ticket URL: <http://trac.macports.org/ticket/15625>
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