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Front End options


Inspired by a recent question and others like it, and not finding an existing duplicate, I ask:





  • What is the hierarchy of Front End options?




  • How do they work?




  • How can their values be set and recalled?





Answer




Option hierarchy


Quoting John Fultz:



Options work on an inheritance model. ... It all starts someplace. That would be the hard-coded option values in the front end C code. The root of the inheritance of options. Then one typically thinks of $FrontEnd as being the next level down, but there's another level in between. That is $DefaultFrontEnd. So, at the global level, it's -> $DefaultFrontEnd -> $FrontEnd -> $FrontEndSession. But only values set to $FrontEnd get written to your preferences file.



In addition to these global settings many Front End options (or their equivalents) can be set at the Notebook level, with e.g. EvaluationNotebook[], and these, when set, take local priority.


Settings made to the Notebook are saved in the Notebook (.nb). Settings made to $FrontEnd are saved in:


FileNameJoin[{$UserBaseDirectory, "FrontEnd", "init.m"}]

Settings to either $FrontEndSession or $DefaultFrontEnd do not persist between sessions. Settings made to $FrontEndSession override those to $FrontEnd for the duration of the session, while $DefaultFrontEnd are only used if the same option is specified nowhere else.



Setting and recalling option values


$FrontEnd and Notebook options can be set and cleared using the Option Inspector with the menu selections Global Preferences and Selected Notebook respectively. To clear an option click the x next to its option name:


enter image description here


Options can be set and recalled at all levels with SetOptions and Options.
For example one could make the following settings:


SetOptions[$DefaultFrontEnd,     FontColor -> Red    ]

SetOptions[$FrontEnd,            FontColor -> Orange ]

SetOptions[$FrontEndSession,     FontColor -> Magenta]


SetOptions[EvaluationNotebook[], FontColor -> Blue   ]

Many options are aslo accessible and configurable through CurrentValue. An unqualified CurrentValue will show the value lowest in the hierarchy (with the highest priority):


CurrentValue[FontColor] // InputForm


RGBColor[0, 0, 1]  (* blue *)

A qualified CurrentValue will show the other settings as well:



CurrentValue[#, FontColor] & /@
  {$DefaultFrontEnd, $FrontEnd, $FrontEndSession} // InputForm


{RGBColor[1, 0, 0],    (* red     *)
 RGBColor[1, 0.5, 0],  (* orange  *)
 RGBColor[1, 0, 1]}    (* magenta *)

The qualified form may be used to set option values:


CurrentValue[EvaluationNotebook[], FontColor] = Green;


If the Notebook option is cleared through the Option Inspector, or a new Notebook is opened, the next setting up the hierarchy is used:


CurrentValue[FontColor] // InputForm


RGBColor[1, 0, 1]

After Mathematica is restarted the $FrontEnd setting persists:


CurrentValue[FontColor] // InputForm



RGBColor[1, 0.5, 0]


As David Creech noted in a comment it is possible to use Inherited as an option value to un-set that option and revert to the next higher level of the hierarchy. Example:


SetOptions[EvaluationNotebook[], FontColor -> Blue]

Options[EvaluationNotebook[]]



{FontColor -> RGBColor[0, 0, 1], FrontEndVersion -> . . .}



SetOptions[EvaluationNotebook[], FontColor -> Inherited]

Options[EvaluationNotebook[]]


{FrontEndVersion -> "10.1 for Microsoft Windows . . .}



Note that the Option has been entirely removed from the Notebook options list.



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