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MathGroup Archive 1998

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Re: Question about FormatType Styles



> What is the purpose of FormatType styles?
> 
> When I type stuff in, the cell has style "Input".  But the FormatType
> style "InputForm" overrides the style settings for the style "Input".
> 
> What is the point of this?  I looked in the option inspector, and the
> FormatType cannot be removed.  So it appears that the style settings
> for "Input" never do anything.  I find this style stuff exceedingly
> complex. Far more complex than any mathematics I have ever seen.

Yes, it is complicated, but it's not completely nonsensical.  In order
to understand why there's a separate FormatType style, I have to lay a
bit of background.  I'm afraid this email's going to be long, so I hope
you'll bear with me.

First, it's not clear to me whether you know what a format type is. Just
in case you don't, I'll explain it.  A format type is basically a a set
of rules that describes how mathematical expressions will look. For
example, TraditionalForm uses 'sin(x)', whereas the others use
'Sin[x]'.  InputForm uses '1/2', whereas OutputForm uses 1 (new line) -
(new line) 2, and Standard and TraditionalForms typeset the fraction.
Each form has a certain visual identity along with the associated
rules, and thus slightly different styles.  So, your statement about
removing the FormatType doesn't really make sense, as there must always
be some set of rules for how to display mathematical input/output for
Input/Output/etc. styles.

Next, we need to to understand that your statement about "style settings
for Input never doing anything" is not correct.

Try changing the text color of the Input style to green.  Voilah...your
input turns green.  Now, try changing the font of the Input style (this
is probably what you've been trying).  Doesn't seem to work.  The
problem here is that the InputForm style has an explicit font setting.
However, the InputForm style has no explicit color setting, so it
inherits the color setting from the Input style.  You can tell whether
a cell has an explicit setting for something by clicking anywhere in
the cell and choosing Format->Show Expression to see the cell contents.
Use this menu option again to restore the cell the way it was before.

Incidentally, the TraditionalForm style has no explicit font setting, so
in fact, any font change you made to the Input style shows up in
TraditionalForm input cells.

Format Type styles can inherit from styles other than Input...for
example, Output, Message, and Print styles.  Yes, the mechanism could
have been implemented by having separate Input-TraditionalForm,
Output-TraditionalForm, Input-StandardForm, Output-StandardForm, etc.
cell styles, but the proliferation of unique, one-shot styles would
probably be more confusing than the inheritance method we're using now.

Another question you might be wondering (as I did when I first learned
this mechanism) is why doesn't the Input cell style have an explicit
font family setting?  Why set to Courier in the StandardForm and
InputForm styles instead?

The answer has to do with inline cells.  Just like format type styles
inherit from cell styles, an inline cell inherits style settings from
its surrounding cells.  Try pasting the following cell expressions with
inline mathematical expressions into a notebook front end:

Cell[TextData[{
  "Theorem 1: ",
  Cell[BoxData[
      FormBox[
        RowBox[{
          RowBox[{
            SuperscriptBox["x", "2"], " ", "+", " ", 
            SuperscriptBox["y", "2"]}], " ", "\[Equal]", " ", 
          SuperscriptBox["z", "2"]}], TraditionalForm]]] }], "Text"]

Now change the entire cell's cell style to Title, or Section.  You'll
notice that the inline cell changes as well.

As I said earlier, the different format types have a certain visual
identity that we've attached to them.  TraditionalForm's identity uses
proportional fonts...in inline cells, it uses the same font the
surroung text uses by default.  StandardForm and InputForm, though, are
identified with monospaced fonts (specifically Courier).  So, if you
create an inline StandardForm cell, the StandardForm style overrides
the inherited cell style's font and chooses Courier instead.  For
example:

Cell[TextData[{
  "Theorem 1: ",
  Cell[BoxData[
      RowBox[{
        RowBox[{
          SuperscriptBox["x", "2"], "+", 
          SuperscriptBox["y", "2"]}], "==", 
        SuperscriptBox["z", "2"]}]],
    ImageMargins->{{0, 0}, {0, 0}}]
}], "Text"]

So, given that for inline cells, we want TraditionalForm to have no
explicit font setting, and we want StandardForm, et. al., to have a
font setting of Courier, the choice to make StandardForm, et. al.,
styles to be explicitly Courier while not setting explicitly the Input
cell style's font makes some sense.

I hope this helps.

> Christopher R. Carlen
> crobc@epix.net          <--- Reply here, please. carlenc@cs.moravian.edu
> My OS is Linux v2


Sincerely,

John Fultz
jfultz@wolfram.com
Front End Group
Wolfram Research, Inc.



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