##########################################################################
   #                                                                        #
   #  STFL - The Structured Terminal Forms Language/Library                 #
   #  Copyright (C) 2006, 2007  Clifford Wolf <clifford@clifford.at>        #
   #                                                                        #
   #  This library is free software; you can redistribute it and/or         #
   #  modify it under the terms of the GNU Lesser General Public            #
   #  License as published by the Free Software Foundation; either          #
   #  version 3 of the License, or (at your option) any later version.      #
   #                                                                        #
   ##########################################################################


STFL - Structured Terminal Forms Language/Library
=================================================

STFL is a library which implements a curses-based widget set for text
terminals. The STFL API can be used from C, SPL, Python, Perl and Ruby. The
public STFL API is only 14 simple function calls big and there are already
generic SWIG bindings. Thus is very easy to port STFL to additional scripting
languages.

A special language (the Structured Terminal Forms Language) is used to
describe STFL GUIs. The language is designed to be easy and fast to write
so an application programmer does not need to spend ages fiddling around
with the GUI and can concentrate on the more interesting programming tasks.

There are two different syntaxes for STFL code, one designed to make
handwriting of STFL code as easy as possible and one aiming at generated
STFL code.

The STFL GUI descriptions (written in STFL code) do not contain any concrete
layouting information such as x/y coordinates of widgets. Instead container
widgets such as vertical and horizontal boxes as well as tables are used to
group widgets and the actual layouting work is done by the STFL library. Thus
STFL GUIs can handle terminals of different sizes and terminal resize events
transparently for the application programmer.


Building and Installing STFL
----------------------------

Simply run 'make' and 'make install'. You might want to edit the Makefile.cfg
file before building and installing STFL.

In order to build a full-featured STFL with all scripting language bindings
enabled you need to have the following packages installed (including the
development packages):

	ncursesw
		The wide-character ncurses library. On some distributions
		this might be part of the ncurses package, on other
		distributions this might be an extra package.

	SWIG
		STFL is using SWIG for generating the Perl, Python and Ruby
		language bindings.

	Perl, Python, Ruby, SPL
		In order to create the language bindings you need to have
		the languages themselves installed.

Since STFL is a wide-character library it will only work on systems which
do have wide-character support in the system libraries. This might not be
the case for in older Linux distributions or other UNIXes.


The Structured Terminal Forms Language
--------------------------------------

STFL Forms consist of (instances of) widgets which are organized in a tree. A
special language - the Structured Terminal Forms Language - can be used to
describe such trees in an efficient and still easy to read and maintain way.

The Structured Terminal Forms Language has only two syntactical constructs:
Variable declarations and widget instantiations. Each widget instantiation
may contain variable declarations and child widget instantiations.

A widget can be instantiated by simply writing down the type of the widget.
Example given:

	vbox

Sometimes one wants to give the instantiated widget a name so the widget
can be easily accessed later. This can be done by appending the widget name
using square brackets:

	label[foobar]

Child widgets are instantiated the same way but must be indented:

	vbox
	  label[label1]
	  label[label2]

Note that one must not use tabs for the indenting. Only blanks are allowed.

Variables are declared like child widgets. A variable consists of a key and
a value, separated by a colon. Values can be quoted using single or double
quotes when they contain blanks.

	vbox
	  label[label1]
	    text:"Hello World!"
	  label[label2]
	    text:"This is a test.."

It is also possible to append an additional name to variables using square
brackets so the application can read and write the variable value:

	vbox
	  label[label1]
	    text[label1_text]:"Hello World!"
	  label[label2]
	    text[label2_text]:"This is a test.."

Usually variables configure the widget they are directly associated with or
store status information from that widget. But sometimes variables contain
information about the relationship of the widget they are directly associated
with and its parent widget. This variables are always start with a dot.

Example given the .border variable can be used to configure the borders of
table cells:

	table
	  label
	    .border:lrtb
	    text:"Hello"
	  label
	    .border:lrtb
	    text:"World!"

Sometimes one wants to set a variable not only for the current widget but also
for all its child widgets. This can be done by prefixing the variable name
with he at-sign. Example given:

	vbox
	  @style_normal:fg=white,bg=blue
	  label
	    text:"White text.."
	  label
	    text:"..on blue background."

This kind of variables can also be defined for only one widget type:

	vbox
	  @style_normal:fg=white,bg=blue
	  @input#style_normal:fg=black,bg=red
	  label
	    text:"White text on blue background."
	  input
	    text:"Black text on red background."

Alternatively it is possible to postfix the widget types with '#classname'
and prefix the variables with 'classname#':

	vbox
	  @style_normal:fg=white,bg=blue
	  @foobar#style_normal:fg=black,bg=red
	  label
	    text:"White text on blue background."
	  input#foobar
	    text:"Black text on red background."

While widget instantiations must always be on a new line, variable declarations
can also be written on the same line as the widget they are for and it is
possible to declare more than one variable in one line:

	table
	  label .border:lrtb text:"Hello"
	  label
	    .border:lrtb text:"World!"

Sometimes one wants to generate STFL code from scripts. In this cases it can
become hard to automatically generate the indenting correctly. For such
situations it is possible to use a different format with curly brackets. The
following two code fragments are identical:

	vbox
	  hbox
	    label
	      .expand:0
	      text:"Foo: "
	    input[foo]
	      text:"Hello"
	  hbox
	    label
	      .expand:0
	      text:"Bar: "
	    input[bar]
	      text:"World!"

	{vbox{hbox{label .expand:0 text:"Foo: "}{input[foo] text:"Hello"}
	{hbox{label .expand:0 text:"Bar: "}{input[bar] text:"World!"}}}

Newline characters are not allowed inside of an STFL code fragment in curly
brackets (the example above is just broken up in two line to improve the
readability). It is even possible to embed an STFL code fragment in curly
brackets in a normal indented code block. Example given:

	vbox
	  {hbox{label .expand:0 text:"Foo: "}{input[foo] text:"Hello"}}
	  {hbox{label .expand:0 text:"Bar: "}{input[bar] text:"World!"}}

It is also possible to include the focus information in STFL code: Simply
prefix the widget which shall have the focus with a '!'. Only one widget
may have the focus at a time.

The STFL parser can also read external files. This can be done by putting the
filename in < > brackets in the STFL file. Note that this is not a verbatim
include but calls another parser instance recursively. So there is an extra
indenting / curly brackets state for the external file.

Comment lines in STFL code start with a '*' character. There must be no
statement in the same line as the comment (i.e. only whitespaces are allowed
before the '*' character). Comment are not allowed within a code fragment
in curly brackets.


The STFL Style Descriptions
---------------------------

STFL is using a generic syntax whenever the style (color, etc.) of a text
can be specified: A comma separated key=value list, where the key can be
'bg' for background, 'fg' for foreground and 'attr' for text attributes.
Example given the following style string can be used for creating bold
blinking white text on blue background:

	bg=blue,fg=white,attr=bold,attr=blink

The following colors are supported:

	black
	red
	green
	yellow
	blue
	magenta
	cyan
	white

And the following attributes:

	standout
	underline
	reverse
	blink
	dim
	bold
	protect
	invis

On terminals that support 256 colors it's also possible to use extended colors,
by using "color<number>" as color name, where "<number>" is a number between
0 and 255. For a complete chart of numbers and their corresponding colors,
please see here: http://www.calmar.ws/vim/256-xterm-24bit-rgb-color-chart.html

The terminal default colors are used when no background or no foreground color
is specified. So keep care when only specifying one value. Example given text
printed using the style string 'fg=white' can't be seen on terminals with a
white default background.


Key and Keybinding Descriptions
-------------------------------

Key descriptions are strings describing a key press event. With some
exceptions this are the return values of the ncurses keyname() and key_name()
functions. The exceptions are:

	ENTER
		The return key has been pressed.

	SPACE
		The space key has been pressed.

	TAB
		The tabulator key has been pressed.

	ESC
		The escape key has been pressed.

	F0 .. F63
		A function key has been pressed.

	UNKNOWN
		An unknown key has been pressed.
		(Usually this is the result of a broken multibyte sequence)

A key binding description is a whitespace-separated list of key descriptions
used in bind_* variables to bind keys to widget actions. Each widget provides
default bindings for all its actions. If you want to extend the list of bind
keys instead of overwriting them you must use the special key-description "**"
in the keybinding description to refer to the default bindings.

Key values can e.g. be dumped using the following little Perl script:

perl -mstfl -le '$_ = stfl::create("label text:\"Press a key\"")->run(0);
stfl::reset(); print;'


The STFL Widget Library
-----------------------

vbox and hbox
~~~~~~~~~~~~~

This widgets simply layouts its child widgets vertically or horizontally
respectively. The following variables are supported by both widgets:

	bind_left, bind_right
		The keybindings in a hbox for changing the focus to the
		next or previous child widget. Default values are the
		LEFT and RIGHT keys.

	bind_up, bind_down
		The keybindings in a vbox for changing the focus to the
		next or previous child widget. Default values are the UP
		and DOWN keys.

	style_normal
		The background style.

	tie
		Tie the box containing the widgets to the specified borders.
		The value is a string containing the characters 'l' (left
		border), 'r' (right border), 't' (top border), 'b' (bottom
		border) and 'c' (center). The default value is 'lrtb'.

	.tie
		Tie this widget within its sub-box to the specified borders.
		The value is using the same syntax as the "tie" variable above.

	.expand
		Contains the information if child widgets should be expanded
		to fit the available space. The value is a string that may
		contain the characters 'v' (for vertical expansion), 'h' (for
		horizontal expansion) and '0' (for no expansion).

		The hbox widget ignores the vertical expansion information and
		the vbox widget the horizontal expansion information.

		The default value is 'vh'.

	.height
		Hardcode the height of this child widget to the specified
		number of lines. Usually one wants to also declare .expand:0
		when declaring this variable.

	.width
		Hardcode the width of this child widget to the specified
		number of characters. Usually one wants to also declare
		.expand:0 when declaring this variable.

	.display
		Simply ignore this child widget if this variable is set to '0'.
		The default value is '1'.

label
~~~~~

A simple text label. The following variables are supported by this widget:

	style_normal
		The style used for displaying the text.

	text
		The text to be displayed

input
~~~~~

A simple input widget for one line of text input. The following variables are
supported by this widget:

	bind_left, bind_right
		Move the cursor left and right. Default values are the LEFT
		and RIGHT keys.

	bind_home
		Move the cursor to the first character. Default values are
		the HOME key or Ctrl-A.
		
	bind_end
		Move the cursor after the last character. Default values are
		the END key or Ctrl-E.

	bind_delete
		Delete the character under the cursor. Default value is the
		DC (DEL) key.

	bind_backspace
		Delete the character before the cursor. Default value is the
		BACKSPACE key.
		
	style_normal
		The style of this widget when it does not have the
		focus.

	style_focus
		The style of this widget when it does have the focus.

	size
		The length (width) of the input box.

	text
		The value displayed in the input box.

	pos
		The current cursor position in the input box.

	offset
		The offset of the text displayed in the input box
		(when the text is larger then the input box).

checkbox
~~~~~~~~

Implementation of a checkbox. The following variables are supported
by this widget:

	bind_toggle
		The keys used to toggle the checkbox value. Default value is
		"ENTER SPACE", meaning the ENTER and SPACE keys.

	style_normal
		The style of this widget when it does not have the
		focus.

	style_focus
		The style of this widget when it does have the focus.

	text_0
		The text displayed when the checkbox' value is 0. Default value
		is "[ ]".

	text_1
		The text displayed when the checkbox' value is 1. Default value
		is "[X]".

	pos
		The cursor position within text_0/text_1. The default value is
		1, which works fine for "[ ]" and "[X]". But for example for
		text_0:"--> <--" and text_1:"==>X<==" you would want to set it
		to 3 instead.

	value
		The checkbox' state (0 or 1).

table
~~~~~

The most important container widget. The special widget 'tablebr' is used to
mark the begin of a new table row. The following variables are supported by
this widget:

	bind_left, bind_right, bind_up, bind_down
		The keybindings for changing the focus within a table.
		Default values are the UP, DOWN, LEFT and RIGHT keys.

	style_normal
		The style for the table borders.

	.expand
		Contains the information if child widgets should be expanded
		to fit the available space. The value is a string that may
		contain the characters 'v' (for vertical expansion), 'h' (for
		horizontal expansion) and '0' (for no expansion).

		Since there is just one width for all cells in a column and
		just one height for all cells in a row it still may happen
		that cells are expanded a bit.

		The default value is 'vh'.

	.height, .width
		Hardcode the height or .width of this table cell to the
		specified number of characters. Usually one wants to also
		declare .expand:0 when declaring one of this variables.

	.colspan, .rowspan
		The number of columns or rows for this cell. Default is '1'.

	.border
		The borders for this cell. This is a string which may contain
		the characters 'l', 'r', 't' and 'b' for left, right, top and
		bottom borders.

	.spacer
		Like .border, but only adds a spacer between the cells.

	.tie
		Tie this table cell within its box to the specified borders.
		The value is a string containing the characters 'l' (left
		border), 'r' (right border), 't' (top border), 'b' (bottom
		border) and 'c' (center). The default value is 'lrtb'.

list
~~~~

The list widget can be used to display a list of items, one per line. The
items are stored as 'listitem' child widgets of the 'list' widget. When
there are more items then the list widget has lines the list widget is
automatically scrolling. The list widget implements the following variables:

	bind_up, bind_down
		The key bindings for scrolling up or down by line. Default
		values are the UP and DOWN keys.

	bind_page_up, bind_page_down
		The key bindings for scrolling up or down by page. Default
		values are the PPAGE (PAGE_UP) and NPAGE (PAGE_DOWN) keys.

	bind_home, bind_end
		The key bindings for moving to top or bottom of list. Default
		values are the HOME and END keys.

	style_focus
		Style of the active list item when the widget has the focus.

	style_selected
		Style of the active list item when the widget has not the
		focus.

	style_normal
		Style of the currently not active list items.

	pos
		The number of the current list item

	pos_name
		The widget name of the current list item.

	offset
		The number of the list item displayed in the first line (this
		becomes >0 when scrolling).


listitem
~~~~~~~~

An in a list widget. Implements the following variables:

	text
		The text displayed in this list item.

textview
~~~~~~~~

A widget for displaying multiline text. The text itself is stored within
listitem child widgets. Implements the following variables:

	bind_up, bind_down
		The key bindings for scrolling up or down by line. Default
		values are the UP and DOWN keys.

	bind_page_up, bind_page_down
		The key bindings for scrolling up or down by page. Default
		values are the PPAGE (PAGE_UP) and NPAGE (PAGE_DOWN) keys.

	bind_home, bind_end
		The key bindings for moving to top or bottom of text. Default
		values are the HOME and END keys.

	style_normal
		The style the text itself is displayed.

	style_end
		The style used for the EOT-Markers.

	offset
		The number of the first line displayed
		(becomes >0 when scrolling).

	richtext
		Set to '1' to enable richtext support

	style_FOOBAR_normal
		The style for text after a <FOOBAR>. the </> token can
		be used to restore the style_normal settings. this variables
		are only used if the 'richtext' variable is set.

textedit
~~~~~~~~

A widget for editing multiline text. The text itself is stored within
listitem child widgets.

	bind_up, bind_down, bind_left, bind_right, bind_page_up, bind_page_down,
	bind_home, bind_end, bind_delete, bind_backspace, bind_enter
		Key bindings for navigating the text. The default values are UP, DOWN,
		LEFT, RIGHT, PPAGE (PAGE_UP), NPAGE (PAGE_DOWN), HOME or Ctrl-A,
		END of Ctrl-E, DC (DEL), BACKSPACE and ENTER keys respectively.

	style_normal
		The style the text itself is displayed.

	style_end
		The style used for the EOT-Markers.

	cursor_x, cursor_y
		Cursor position within the text

	scroll_x, scroll_y
		Current offset for horizontal and vertical scrolling

Common Variables
----------------

There are some variables which are used by the STFL core to configure some
widget-independent features.

modal
~~~~~

A widget which has the modal variable set to '1' will not pass any events
to its parent widgets. Either the event is handled by the widget itself or
it is returned directly to the caller of stfl_run().

autobind
~~~~~~~~

Setting autobind to '0' disables all automatically assigned keybindings for
this widget. Actions which aren't set explicitly bind to keys using the
bind_* variables are left unbind and can't be triggered using the user
interface. Setting autobind to '0' does not prevent typing of regular text
into input and textedit widgets; for such functionality see 'process'. 

process
~~~~~~~~

Setting process to '0' disables all keypress processing on the widget and
passes the keypress events to the caller of stfl_run(). This setting is
similar to autobind, but it will stop all key processing on the widget,
including typing of regular text into input and textedit widgets. When
this variable is set back to '1', processing resumes as usual.

on_*
~~~~

The on_* variables can be used to catch keypresses in this widget and return
the value of the on_* variable to the caller of stfl_run(). The on_* variables
are evaluated before the keypresses are passed to the widget. The '*' part
of the on_* variables is a key description. E.g. "on_^X:foobar" will let
stfl_run() return the string "foobar" when Ctrl-X is being pressed.

can_focus
~~~~~~~~~

Setting can_focus to '0' on a widget will make it non-focusable, even if
it is a widget that could otherwise have focus (input, listitem, etc.).
The widget is still focusable manually by prefixing it with a '!' or
using stfl_set_focus().


The Common STFL Scripting Language API
--------------------------------------

STFL has a big C-API which allows a wide range of in-depth operations on
widget trees. But most of this C-API is only needed for writing new STFL
widgets. The common STFL scripting language API only has a small number of
functions and besides the 'form handlers' this functions do only operate
on read-only scalar values, so it is pretty easy to write additional bindings
for scripting languages not yet supported by STFL.

C API Notes
~~~~~~~~~~~

All functions listed here are also available through the STFL C-API.

All strings returned by stfl functions are constant and must not be freed or
modified by the caller. When the caller wants to preserve a string for longer
than until the next stfl function call the caller must copy the strings.

All strings passed to STFL functions are considered read-only by STFL and
are neither modified nor freed by STFL.

The functions which may return an null value will return a null-pointer
in C. All string parameters which are null-pointers are interpreted as they
where empty strings.

Unicode Support
~~~~~~~~~~~~~~~

The STFL C Library handles all strings as wide character strings (wchar_t*). So
the STFL library itself has complete Unicode support.

All current scripting language bindings convert all strings passed between STFL
and the scripting language to UTF-8.

Programs using STFL directly might use the STFL "ipool" API for easy conversion
between wide characters and other encodings.

SPL API Notes
~~~~~~~~~~~~~

The stfl_free() function is not implemented in SPL because the SPL garbage
collector does call the low-level STFL free function automatically. The
stfl_reset() function is automatically called when the STFL module is unloaded
(i.e. on program termination).

The stfl_quote() function can also be called using the name encode_stfl() so
it can be used with the SPL encoding/quoting operator (::).

Python API Notes
~~~~~~~~~~~~~~~~

The stfl_free() function is not implemented in Python because the garbage
collector does call the low-level STFL free function automatically. The
stfl_reset() function is automatically called on program termination.

The functions which take a form as first parameter can also be called as method
of the form. All functions are in the "stfl" namespace, so the "stfl_" prefix
for the function names is replaced with "stfl." in python.

Perl API Notes
~~~~~~~~~~~~~~

The stfl_free() function is not implemented in Perl because the garbage
collector does call the low-level STFL free function automatically. The
stfl_reset() function is automatically called on program termination.

The functions which take a form as first parameter can also be called as method
of the form. All functions are in the "stfl" namespace, so the "stfl_" prefix
for the function names is replaced with "stfl::" in perl.

Ruby API Notes
~~~~~~~~~~~~~~

The stfl_free() function is not implemented in Perl because the garbage
collector does call the low-level STFL free function automatically. The
stfl_reset() function is automatically called on program termination.

The functions which take a form as first parameter can also be called as method
of the form. All functions are in the "Stfl" namespace, so the "stfl_" prefix
for the function names is replaced with "Stfl." in ruby.

stfl_create(text)
~~~~~~~~~~~~~~~~~

Parses the the STFL description text passed as parameter and returns a form
handler. Most of the following functions expect such a form handler as first
parameter.

stfl_free(form)
~~~~~~~~~~~~~~~

Free all resources associated with this form. On languages with a garbage
collector calling this function is optional and might even be implemented
as no-op.

stfl_run(form, timeout)
~~~~~~~~~~~~~~~~~~~~~~~

Return the next event. If no more prior generated events are waiting display
the form and process one input character. The event string can be an null
value when something changed in the form (e.g. the user changed the focus of
the current widget) but all inputs have been handled internally inside of STFL.
The event string can be "TIMEOUT" when the timeout has been reached, a key
description is key has been pressed that is not being handled internally in
STFL or the value of an on_* variable can be returned if a keypress has been
caught using such a variable.

The 2nd parameter is a timeout in ms. When no key has been pressed until this
timeout has been reached the function returns with a "TIMEOUT" event. Set this
parameter to 0 to disable the timeout.

When the timeout parameter is set to -1 the form is displayed independent of
the current status of the event queue and the function returns right after
displaying the form without handling any input characters. In this mode always
an null value is returned.

When the timeout parameter is set to -2 the displayed is not updated and the
next pending event is returned. If there are no pending events an null
value is returned.

When the timeout parameter is set to -3, rendering (and setting the :x, :y, :w
and :h pseudo-variables) is done but the screen is not updated and no events
are fetched. This is useful for incrementing rendering processes where
appropriate :x, :y, :w and/or :h values are needed for finishing the layout.

stfl_redraw()
~~~~~~~~~~~~

The stfl_run() function automatically refreshes the screen on each run.
This function can be used to instruct stfl_run() to completely redraw the
screen on its next run, instead of just refreshing. This feature is useful
when another program has printed unwanted text to the terminal and a full
redraw is needed. In most programs that support "clear screen" feature, it
is made available on Ctrl+L.

stfl_reset()
~~~~~~~~~~~~

The stfl_run() function automatically activates ncurses. This function
can be used to explicitly switch back to normal text mode. In some
languages this is automatically done on program termination.

stfl_get(form, name)
~~~~~~~~~~~~~~~~~~~~

Returns the current value of the specified variable. When the variable does not
exist this function returns an null value.

stfl_set(form, name, value)
~~~~~~~~~~~~~~~~~~~~~~~~~~~

This sets the specified variable to the specified value.

stfl_get_focus(form)
~~~~~~~~~~~~~~~~~~~~

Returns the name of the widget which currently has the focus or an null
value when the widget having the focus has no name.

stfl_set_focus(form, name)
~~~~~~~~~~~~~~~~~~~~~~~~~~

Set the focus to the specified widget.

stfl_quote(text)
~~~~~~~~~~~~~~~~

Quote the text so it can be safely used as variable value in STFL code.

stfl_dump(form, name, prefix, focus)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Return the subtree starting with the widget specified in the 2nd parameter as
STFL code fragment. The entire form is return when the 2nd parameter is an
empty string or null. All widget and variable names in the dump are
prefixed with the string in the 3rd parameter. The information which widget has
the focus is also included in the dump when the 4th parameter is an integer
not equal 0.

The function returns an null value when there was an error.

stfl_text(form, name)
~~~~~~~~~~~~~~~~~~~~~

Return the concatenation of all "listitem text" variables under the specified
widget. This is useful for reading the text in "textedit" widgets.

The function returns an null value when there was an error.

stfl_modify(form, name, mode, text)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Import the STFL code specified in the 4th parameter to an existing form. The
2nd parameter is used to specify a widget which is used as starting point for
the modification. The 3rd parameter is a string specifying how the new STFL
code should be added to the widget tree:

	delete
		Delete the widget. The 4th parameter is ignored in this mode.

	replace
		Replace the widget in the tree with the new tree.

	replace_inner
		Replace the child list of the widget with the child list
		of the root element of the new tree.

	insert
		Add the new tree at the begin of the child list of the widget.

	insert_inner
		Add the child list of the root element of the new tree at the
		begin of the child list of the widget.

	append
		Add the new tree at the end of the child list of the widget.

	append_inner
		Add the child list of the root element of the new tree at the
		end of the child list of the widget.

	before
		Add the new tree before the widget.

	before_inner
		Add the child list of the root element of the new tree before
		the widget.

	after
		Add the new tree after the widget.

	after_inner
		Add the child list of the root element of the new tree after
		the widget.

The widget type of the root element of the tree passed in the 4th parameter
doesn't matter in the *_inner modes.

stfl_error()
~~~~~~~~~~~~

Return the error status of the last STFL call. This is null when no error
occurred and the error message otherwise. An error could e.g. be a parser
error for broken STFL code.

WARNING: This is a planned feature! This version of STFL simply calls abort()
if an internal error is caught.

stfl_error_action(mode)
~~~~~~~~~~~~~~~~~~~~~~~

Set the error handling algorithm. The following strings are valid as mode
parameter:

	abort
		Print error message to stderr and call the abort() function.

	exit
		Print error message to stderr and call exit(1).

	print
		Print error message to stderr and continue execution.

	interactive
		Display a little menu and let the user decide what to do.

	none
		Do nothing - just continue program execution.

The default mode is "interactive".

WARNING: This is a planned feature! This version of STFL simply calls abort()
if an internal error is caught.


Pseudo Variables
----------------

When a widget has a name (declared using the 'widget[name]' syntax in the STFL
code), there are also some special pseudo-variables which can only be accessed
for reading. Note that this pseudo-variables do only have valid values after
the widget has been drawn already. So it is always a good idea to run
stfl_run() with a timeout of -1 before accessing the pseudo-variables.

widgetname:x
~~~~~~~~~~~~

The absolute x-position of the widget on the screen. (from the left border)

widgetname:y
~~~~~~~~~~~~

The absolute y-position of the widget on the screen. (from the upper border)

widgetname:w
~~~~~~~~~~~~

The width of the widget.

widgetname:h
~~~~~~~~~~~~

The height of the widget.

widgetname:minw
~~~~~~~~~~~~~~~

The minimal width (i.e. before expanding) of the widget.

widgetname:minh
~~~~~~~~~~~~~~~

The minimal height (i.e. before expanding) of the widget.


TODOs
-----

- Implement so far unimplemented widgets
- Missing error handling and reporting