The command line needs to obey a grammar.  It is then against this grammar that
bugs will be identified.

Conventions:
  - Literals are double-quoted.
  - "*", "+" and "?" suffixes have POSIX semantics.
  - Low-level primitives are in <brackets>.
  - @reports for dynamic lists such as custom report names.


The general form of commands is:

  task [ all-commands ]


This breaks down into a supported grammar:

  command         ::= all-commands?
                    ;

  all-commands    ::= custom-report
                    | read-command
                    | write-command
                    | special-command
                    ;

  custom-report   ::= filter? @report ;
  read-command    ::= ;
  write-command   ::= ;
  special-command ::= ;

  filter          ::= expression ;

  expression      ::= ;

Dynamic lists:

  @report         ::= all custom reports ;

Low-level:

  dom             ::= context-value
                    | system-value
                    | rc-value
                    | task-value
                    ;

  context-value   ::= "context.program"
                    | "context.args"
                    | "context.width"
                    | "context.height"
                    ;

  system-value    ::= "system.version"
                    | "system.os"
                    ;

  rc-value        ::= "rc." name
                    ;

  task-value      ::= <id> "." attribute
                    | <uuid> "." attribute
                    ;
             
  literal         ::= <string>
                    | <numeric>
                    | <date>
                    | <duration>
                    ;

Supported primitives:

  <id>
  <uuid>
  <override>
  <string>
  <numeric>
  <date>
  <duration>



---

Default:
  task

Custom reports:
  task <filter> active
  task <filter> all
  task <filter> blocked
  task <filter> blocking
  task <filter> completed
  task <filter> list
  task <filter> long
  task <filter> ls
  task <filter> minimal
  task <filter> newest
  task <filter> next
  task <filter> oldest
  task <filter> overdue
  task <filter> ready
  task <filter> recurring
  task <filter> unblocked
  task <filter> waiting

Build-in read-only:
  task <filter> burndown.daily
  task <filter> burndown.monthly
  task <filter> burndown.weekly
  task          calendar [due|<month> <year>|<year>] [y]
  task          colors [sample | legend]
  task          columns [substring]
  task <filter> count
  task          diagnostics
  task          execute <external command>
  task <filter> export
  task <filter> ghistory.annual
  task <filter> ghistory.monthly
  task          help
  task <filter> history.annual
  task <filter> history.monthly
  task <filter> ids
  task <filter> information
  task          logo
  task <filter> projects
  task          reports
  task          show [all | substring]
  task <filter> stats
  task <filter> tags
  task          timesheet [weeks]
  task          udas
  task <filter> uuids
  task          version
  task          _aliases
  task          _columns
  task          _commands
  task          _config
  task <filter> _ids
  task <filter> _projects
  task          _show
  task <filter> _tags
  task          _udas
  task <filter> _urgency
  task <filter> _uuids
  task          _version
  task          _zshcommands
  task <filter> _zshids
  task <filter> _zshuuids

Write commands:
  task          add <mods>
  task <filter> annotate <mods>
  task <filter> append <mods>
  task          config [name [value | '']]
  task <filter> delete <mods>
  task <filter> denotate <pattern>
  task <filter> done <mods>
  task <filter> duplicate <mods>
  task <filter> edit
  task          import <file> [<file> ...]
  task          log <mods>
  task          merge <URL>
  task <filter> modify <mods>
  task <filter> prepend <mods>
  task          pull <URL>
  task          push <URL>
  task <filter> start <mods>
  task <filter> stop <mods>
  task <filter> summary
  task          synchronize
  task          undo