---+ Package =TWiki::Prefs=

The Prefs class is a singleton that implements management of preferences.
It uses a stack of TWiki::Prefs::PrefsCache objects to store the
preferences for global, web, user and topic contexts, and provides
the means to look up preferences in these.

Preferences from different places stack on top of each other, so there
are global preferences, then site, then web (and subweb and subsubweb),
then topic, included topic and so on. Each level of the stack is tagged with
a type identifier.

The module also maintains a separate of the preferences found in every topic
and web it reads. This supports the lookup of preferences for webs and topics
that are not on the stack, and must not be chained in (you can't allow
a user to override protections from their home topic!)


%TOC%

---++ ClassMethod *new* <tt>($session[,$cache])</tt>

Creates a new Prefs object. If $cache is defined, it will be
pushed onto the stack.



---++ ObjectMethod *finish* <tt></tt>
Complete processing after the client's HTTP request has been responded
to. 
   1 breaking circular references to allow garbage collection in persistent
     environments



---++ ObjectMethod *pushGlobalPreferences* <tt>()</tt>
Add global preferences to this preferences stack.



---++ ObjectMethod *pushPreferences* <tt>($web,$topic,$type)</tt>
   * =$web= - web to read from
   * =$topic= - topic to read
   * =$type= - DEFAULT, SITE, USER, SESSION, WEB, TOPIC or PLUGIN
   * =$prefix= - key prefix for all preferences (used for plugins)
Reads preferences from the given topic, and pushes them onto the
preferences stack.



---++ ObjectMethod *pushWebPreferences* <tt>($web)</tt>

Pushes web preferences. Web preferences for a particular web depend
on the preferences of all containing webs.



---++ ObjectMethod *pushPreferencesValues* <tt>($type,\%values)</tt>
Push a new preference level using type and values given



---++ ObjectMethod *mark* <tt>()</tt>
Return a marker representing the current top of the preferences
stack. Used to remember the stack when new web and topic preferences
are pushed during a topic include.



---++ ObjectMethod *resetTo* <tt>($mark)</tt>
Resets the preferences stack to the given mark, to recover after a topic
include.



---++ ObjectMethod *getPreferencesValue* <tt>($key) -> $value</tt>
   * =$key - key to look up

Returns the value of the preference =$key=, or undef.

Looks up local preferences when the level
topic is the same as the current web,topic in the session.



---++ ObjectMethod *isFinalised* <tt>($key)</tt>
Return true if $key is finalised somewhere in the prefs stack



---++ ObjectMethod *getTopicPreferencesValue* <tt>($key,$web,$topic) -> $value</tt>

Recover a preferences value that is defined in a specific topic. Does
not recover web, user or global settings.

Intended for use in protections mechanisms, where the order doesn't match
the prefs stack.



---++ getTextPreferencesValue( $key, $text, $meta, $web, $topic ) -> $value
Get a preference value from the settings in the text (and/or optional $meta).
The values read are *not* cached.


---++ ObjectMethod *getWebPreferencesValue* <tt>($key,$web) -> $value</tt>

Recover a preferences value that is defined in the webhome topic of
a specific web.. Does not recover user or global settings, but
does recover settings from containing webs.

Intended for use in protections mechanisms, where the order doesn't match
the prefs stack.



---++ObjectMethod stringify() -> $text

Generate a TML-formatted version of the current preferences

