.TH "tkhtml" "3tcl" "Sun Nov 11 18:57:26 EST 2012"


.SH "NAME"
tkhtml \- Widget to render html documents.

.SH "SYNOPSIS"
html pathName ?options?

.SH "STANDARD OPTIONS"
.RS

.nf
\-height
\-width
\-xscrollcommand   
\-xscrollincrement
\-yscrollcommand   
\-yscrollincrement
.fi
.RE

See the options(n) manual entry for details on the standard options.

.SH "WIDGET-SPECIFIC OPTIONS"
Command-Line Name:-defaultstyle
 .br
Database Name:  defaultstyle
 .br
Database Class: Defaultstyle
 .br
 .RS
 .PP
This option is used to set the default style-sheet for the
widget. The option value should be the entire text of the
default style-sheet.

The default stylesheet defines things that are "built-in" to
the document \- for example the behaviour of <p> or <img> tags
in html. The idea behind making it flexible is to allow
Tkhtml to display anything that looks roughly like an XML
document. But this will not work at the moment because of
other assumptions the implementation makes about the set
of valid tags. Currently, only valid HTML tags are recognized.

The Tkhtml package adds the [::tkhtml::htmlstyle] command to
the interpreter it is loaded into. Invoking this command
returns a CSS document suitable for use with Tkhml as a default
stylesheet for HTML documents. If the \-quirks option is
passed to [::tkhtml::htmlstyle] then the returned document
includes some extra rules used when rendering legacy documents.

If the value of the \-defaultstyle option is changed, the new
value does not take effect until after the next call to the
widget [reset] method.

The default value of this option is the same as the string
returned by the [::tkhtml::htmlstyle] command.
 .RE
Command-Line Name:-fontscale
 .br
Database Name:  fontscale
 .br
Database Class: Fontscale
 .br
 .RS
 .PP
This option is set to a floating point number, default 1.0.
After CSS algorithms are used to determine a font size,
it is multiplied by the value of this option. Setting this
to a value other than 1.0 breaks standards compliance.
 .RE
Command-Line Name:-fonttable
 .br
Database Name:  fonttable
 .br
Database Class: Fonttable
 .br
 .RS
 .PP
This option must be set to a list of 7 integers. The first
integer must be greater than 0 and each subsequent integer 
must be greater than or equal to its predecessor.

The seven integers define the sizes of the Tk fonts (in points)
used when a CSS formatted document requests font-size
"xx-small", "x-small", "small", "medium", "large", "x-large" or
"xx-large", respectively.

The default value is {8 9 10 11 13 15 17}.
 .RE
Command-Line Name:-forcefontmetrics
 .br
Database Name:  forcefontmetrics
 .br
Database Class: Forcefontmetrics
 .br
 .RS
 .PP
This is a boolean option. If true, the font-metrics returned
by Tk are overridden with calculated values based on the
font requested. This improves CSS compatibility, but on some
systems may cause problems. The default is true.
 .RE
Command-Line Name:-forcewidth
 .br
Database Name:  forcewidth
 .br
Database Class: Forcewidth
 .br
 .RS
 .PP
When determining the layout of a document, Tkhtml3 (and all
other HTML/CSS engines) require as an input the width of
the containing block for the whole document. For web-browsers,
this is usually the width of the viewport in which the document
will be displayed.

If this option is true or the widget window is not mapped, 
Tkhtml3 uses the value of the \-width option as the initial
containing block width. Otherwise, the width of the widget
window is used.

The default value is false.
 .RE
Command-Line Name:-imagecache
 .br
Database Name:  imagecache
 .br
Database Class: Imagecache
 .br
 .RS
 .PP
This boolean option (default true) determines whether or not
Tkhtml3 caches the images returned to it by the \-imagecmd
callback script. If true, all images are cached until the
next time the [reset] sub-command is invoked. If false,
images are discarded as soon as they are not in use.

For simple applications, or applications that retrieve 
images from local sources, false is usually a better value
for this option (since it may save memory). However for
web-browser applications where the background images of
elements may be modified by mouseover events and so on, 
true is a better choice.
 .RE
Command-Line Name:-imagecmd
 .br
Database Name:  imagecmd
 .br
Database Class: Imagecmd
 .br
 .RS
 .PP
As well as for replacing entire document nodes (i.e. <img>),
images are used in several other contexts in CSS formatted
documents, for example as list markers or backgrounds. If the
 \-imagecmd option is not set to an empty string (the default),
then each time an image URI is encountered in the document, it
is appended to the \-imagecmd script and the resulting list
evaluated.

The command should return either an empty string, the name of a
Tk image, or a list of exactly two elements, the name of a Tk
image and a script. If the result is an empty string, then no
image can be displayed. If the result is a Tk image name, then
the image is displayed in the widget. When the image is no
longer required, it is deleted. If the result of the command is
a list containing a Tk image name and a script, then instead of
deleting the image when it is no longer required, the script is
evaluated.

If the size or content of the image are modified while it is in
use the widget display is updated automatically.
 .RE
Command-Line Name:-mode
 .br
Database Name:  mode
 .br
Database Class: Mode
 .br
 .RS
 .PP
This option may be set to "quirks", "standards" or 
"almost standards", to set the rendering engine mode. The
default value is "standards".

TODO: List the differences between the three modes in Tkhtml.
 .RE
Command-Line Name:-parsemode
 .br
Database Name:  parsemode
 .br
Database Class: Parsemode
 .br
 .RS
 .PP
This option may be set to "html", "xhtml" or "xml", to set 
the parser mode. The default value is "html".

In "html" mode, the parser attempts to mimic the tag-soup
approach inherited by modern web-browsers from the bad old
days. Explicit XML style self-closing tags (i.e. closing
a markup tag with "/>" instead of ">") are not handled
specially. Unknown tags are ignored.

"xhtml" mode is the same as "html" mode except that explicit
self-closing tags are recognized.

"xml" mode is the same as "xhtml" mode except that unknown
tag names and XML CDATA sections are recognized.
 .RE
Command-Line Name:-shrink
 .br
Database Name:  shrink
 .br
Database Class: Shrink
 .br
 .RS
 .PP
This boolean option governs the way the widgets requested width
and height are calculated. If it is set to false (the default),
then the requested width and height are set by the \-width
and \-height options as per usual.

If this option is set to true, then the widgets requested width
and height are determined by the current document. Each time
the document layout is calculated, the widgets requested height
and width are set to the size of the document layout. If the
widget is unmapped when the layout is calculated, then the
value of the \-width option is used to determine the width
of the initial containing block for the layout. Otherwise, the
current window width is used.
 .RE
Command-Line Name:-zoom
 .br
Database Name:  zoom
 .br
Database Class: Zoom
 .br
 .RS
 .PP
This option may be set to any floating point number. Before
the document layout is calculated, all lengths and sizes
specified in the HTML document or CSS style configuration,
implicit or explicit, are multiplied by this value.

The default value is 1.0.
 .RE
Command-Line Name:-logcmd
 .br
Database Name:  logcmd
 .br
Database Class: Logcmd
 .br
 .RS
 .PP
This option is used for debugging the widget. It is not
part of the official interface and may be modified or
removed at any time. Don"t worry about it.
 .RE
Command-Line Name:-timercmd
 .br
Database Name:  timercmd
 .br
Database Class: Timercmd
 .br
 .RS
 .PP
This option is used for debugging the widget. It is not
part of the official interface and may be modified or
removed at any time. Don"t worry about it.
 .RE
Command-Line Name:-layoutcache
 .br
Database Name:  layoutcache
 .br
Database Class: Layoutcache
 .br
 .RS
 .PP
This option is used for debugging the widget. It is not
part of the official interface and may be modified or
removed at any time. Don"t worry about it.

If this boolean option is set to true, then Tkhtml caches 
layout information to improve performance when the layout of a
document must be recomputed. This can happen in a variety of
situations, for example when extra text is appended to the
document, a new style is applied to the document, a dynamic CSS
selector (i.e. :hover) is activated, the widget window is
resized, or when the size of an embedded image or Tk window
changes.

Layout caching consumes no extra memory or significant
processing cycles, so in an ideal world there is no real reason
to turn it off. But it can be a source of layout bugs, hence
this option.

The default value is true.
 .RE

.SH "DESCRIPTION"

The [html] command creates a new window (given by the pathName
argument) and makes it into an html widget. The html command
returns its pathName argument. At the time this command is invoked,
there must not exist a window named pathName, but pathName"s parent
must exist.

.SH "WIDGET COMMAND"
The [html] command creates a new Tcl command whose name is
pathName. This command may be used to invoke various operations on
the widget as follows:

pathName bbox nodeHandle
.br
.RS
If node nodeHandle generates content, this command returns a
list of four integers that define the bounding-box of the
generated content, relative to the top-left hand corner of the
rendered document. The first two integers are the x and y
coordinates of the top-left corner of the bounding-box, the
later two are the x and y coordinates of the bottom-right
corner of the same box. If the node does not generate content,
then an empty string is returned.
.RE

pathName cget option
.br
.RS
Returns the current value of the configuration option given
by option. Option may have any of the values accepted by
the [html] command.
.RE

pathName configure ?option? ?value?
.br
.RS
Query or modify the configuration options of the widget. If
no option is specified, returns a list describing all of
the available options for pathName (see Tk_ConfigureInfo
for information on the format of this list). If option is
specified with no value, then the command returns a list
describing the one named option (this list will be
identical to the corresponding sublist of the value
returned if no option is specified). If one or more
option-value pairs are specified, then the command modifies
the given widget option(s) to have the given value(s); in
this case the command returns an empty string. Option may
have any of the values accepted by the [html] command.
.RE

pathName fragment html-text
.br
.RS
TODO: Document this command.
.RE

pathName handler node tag script
.br
pathName handler attribute tag script
.br
pathName handler script tag script
.br
pathName handler parse tag script
.br
.RS
This command is used to define "handler" scripts \- Tcl
callback scripts that are invoked by the widget when
document elements of specified types are encountered. The
widget supports two types of handler scripts: "node" and
"script".

For a "node" handler script, whenever a document element
having the specified tag type (e.g. "p" or "link") is
encountered during parsing, then the node handle for the
node is appended to script and the resulting list
evaluated as a Tcl command. See the section "NODE COMMAND"
for details of how a node handle may be used to query and
manipulate a document node. A node handler is called only
after the subtree rooted at the node has been completely 
parsed.

If the handler script is a "script" handler, whenever a
document node of type tag is parsed, two arguments are
appended to the specified script before it is evaluated.
The first argument is a key-value list (suitable for passing 
to the [array set] command containing the HTML attributes
that were part of the element declaration. The second
argument is the literal text that appears between the 
start and end tags of the element. 

Elements for which a "script" handler is evaluated are not
included in the parsed form of the HTML document. Instead,
the result of the script handler evaluation is substituted
into the document and parsed. For example, to handle the
following embedded javascript:
.RS

.nf
<SCRIPT>
  document.write("<p>A paragraph</p>")
</SCRIPT>
.fi
.RE

a script handler that returns the string "<p>A paragraph</p>"
must be configured for nodes of type "SCRIPT".

Unlike node or script handlers, a "parse" handler may be
associated with a specific opening tag, a closing tag or 
with text tags (by specifying an empty string as the tag
type). Whenever such a tag is encountered the parse handler
script is invoked with two arguments, the node handle for
the created node and the character offset of the in the parsed
document. For a closing tag (i.e. "/form") an empty string
is passed instead of a node handle.

TODO: Describe "attribute" handlers.

TODO: The offset values passed to parse handler scripts 
currently have problems. See http://tkhtml.tcl.tk/cvstrac/tktview?tn=126

Handler callbacks are always made from within 
[pathName parse] commands. The callback for a given node
is made as soon as the node is completely parsed.  This can
happen because an implicit or explicit closing tag is
parsed, or because there is no more document data and the
\-final switch was passed to the [pathName parse]
command.

TODO: Return values of handler scripts? If an exception
occurs in a handler script?
.RE

pathName image
.br
.RS
This command returns the name of a new Tk image containing 
the rendered document. Where Tk widgets would be mapped in a 
live display, the image contains blank space.

The returned image should be deleted when the script has 
finished with it, for example:
.RS

.nf
set img [.html image]
# ... Use $img ...
image delete $img
.fi
.RE

This command is included mainly for automated testing and 
should be used with care, as large documents can result in very
large images that take a long time to create and use vast
amounts of memory.

Currently this command is not available on windows. On that
platform an empty string is always returned.
.RE

pathName node ? ?-index? x y?
.br
.RS
This command is used to retrieve one or more document node
handles from the current document. If the x and y parameters
are omitted, then the handle returned is the root-node of the
document, or an empty string if the document has no root-node
(i.e. an empty document).

If the x and y arguments are present, then a list of node 
handles is returned. The list contains one handle for each
node that generates content currently located at viewport
coordinates (x, y). Usually this is only a single node, but
floating boxes and other overlapped content can cause
this command to return more than one node.  If no content is
located at the specified coordinates or the widget window is
not mapped, then an empty string is returned. 

If the \-index option is specified along with the x and y 
coordinates, then instead of a list of node handles, a list of
two elements is returned. The first element of the list is the
node-handle associated with the generated text closest to 
the specified (x, y) coordinates. The second list value is a
byte (not character) offset into the text obtainable by 
[nodeHandle text] for the character closest to coordinates
(x, y). The index may be used with the [pathName tag] commands.

The document node can be queried and manipulated using the
interface described in the "NODE COMMAND" section.
.RE

pathName parse ?-final? html-text
.br
.RS
Append extra text to the end of the (possibly empty)
document currently stored by the widget. 

If the \-final option is present, this indicates that the
supplied text is the last of the document. Any subsequent
call to [pathName parse] before a call to 
[pathName reset] will raise an error. 

If the \-final option is not passed to [pathName parse] along
with the final part of the document text, node handler scripts
for any elements closed implicitly by the end of the document
will not be executed. It is not an error to specify an empty
string for the html-text argument.
.RE

pathName preload uri
.br
.RS
This command is only useful if the \-imagecache option is
set to true and an \-imagecmd script is defined. It causes
the widget to invoke the \-imagecmd script to retrieve
the image at URI uri. Assuming \-imagecache is true, the
returned image is then stored in the image-cache.

This command may be useful when implementing scripting
environments that support "preloading" of images.
.RE

pathName reset
.br
.RS
This is used to clear the internal contents of the widget
prior to parsing a new document. The widget is reset such
that the document tree is empty (as if no calls to 
[pathName parse] had ever been made) and no stylesheets
except the default stylesheet are loaded (as if no
invocations of [pathName style] had occured).
.RE

pathName search selector
.br
.RS
The selector argument passed to this command must be a valid
CSS selector, for example "h1" or "a[href]". This command
returns a list of node-handles corresponding to the set of
document nodes that match the supplied selector.
.RE

pathName style ?options? stylesheet-text
.br
.RS
Add a stylesheet to the widgets internal configuration. The
stylesheet-text argument should contain the text of a
complete stylesheet.  Incremental parsing of stylesheets is
not supported, although of course multiple stylesheets may
be added to a single widget.

The following options are supported:
.RS

.nf
Option                   Default Value
\--------------------------------------
\-id <stylesheet-id>      "author"
\-importcmd <script>      ""
\-urlcmd    <script>      ""
.fi
.RE

The value of the \-id option determines the priority taken
by the style-sheet when assigning property values to
document nodes (see chapter 6 of the CSS specification for
more detail on this process).  The first part of the
style-sheet id must be one of the strings "agent", "user"
or "author". Following this, a style-sheet id may contain
any text.  

When comparing two style-ids to determine which stylesheet
takes priority, the widget uses the following approach: If
the initial strings of the two style-id values are not
identical, then "user" takes precedence over "author", and
"author" takes precedence over "agent". Otherwise, the
lexographically largest style-id value takes precedence.
For more detail on why this seemingly odd approach is
taken, please refer to the "STYLESHEET LOADING" below.

The \-importcmd option is used to provide a handler script
for @import directives encountered within the stylesheet
text. Each time an @import directive is encountered, if the
\-importcmd option is set to other than an empty string, the
URI to be imported is appended to the option value and the
resulting list evaluated as a Tcl script. The return value
of the script is ignored. If the script raises an error,
then it is propagated up the call-chain to the 
[pathName style] caller.

The \-urlcmd option is used to supply a script to translate
"url(...)" CSS attribute values. If this option is not set to
"", each time a url() value is encountered the URI is appended
to the value of \-urlcmd and the resulting script evaluated. The
return value is stored as the URL in the parsed stylesheet.
.RE

pathName tag add tag-name node1 index1 node2 index2
.br
pathName tag remove tag-name node1 index1 node2 index2
.br
pathName tag configure tag-name option value ?option value...?
.br
pathName tag delete tag-name
.br
.RS
The [pathName tag] command is used to highlight regions
of text displayed by the widget. For example, a region
of text selected using the pointer.

Each displayed document character is identified by a 
text node-handle (see below) and an index into the text
returned by the [node text] command. The index is a byte
(not character) offset. See also the documentation for the 
[pathName node \-index] command.  Both the [pathName tag add]
and [pathName tag remove] use this convention.

Evaluating the [pathName tag add] command adds the specified
tag to all displayed characters between the point in the 
document described by (node1, index1) and the point
described by (node2, index2). If the specified tag does
not exist, it is created with default option values. The
order in which the two specified points occur in the
document is not important.

The [pathName tag remove] command removes the specified tag
from all displayed characters between the point in the document
described by (node1, index1) and the point described by
(node2, index2). 

The [pathName tag configure] command is used to configure
a tags options, which determine how tagged characters are
displayed. If the specified tag does not exist, it is
created. The following options are supported:
.RS

.nf
Option                   Default Value
\--------------------------------------
\-background              black
\-foreground              white
.fi
.RE

A tag can be completely deleted (removed from all characters
and have it"s option values set to the defaults) using the 
[pathName tag delete] command.

The [pathName tag] command replaces the 
[pathName select] command that was present in early
alpha versions of Tkhtml3. Users should note that the
options supported by [pathName tag configure] are likely
to change before beta release. See 
                http://tkhtml.tcl.tk/cvstrac/tktview?tn=73 (ticket #73).
.RE

pathName text bbox node1 index1 node2 index2
.br
pathName text index offset ?offset...?
.br
pathName text offset node index
.br
pathName text text
.br
.RS
The [pathName text] commands allow an application to
query and interact with the text of the displayed document.
This can be used, for example, to search for a string
within an Html document, or to copy a region of text
to the system clipboard.

The [pathName text text] command returns a string 
containing the raw, unformatted text of the displayed document.
Each block box is separated from the next by a newline
character. Each block of whitespace is collapsed to a
single space, except within blocks with the CSS "white-space"
property set to "pre".

The [pathName text index] command is used to transform
from a character offset in the string returned by 
[pathName text text] to a node/index pair that can be
used with the [pathName tag] commands. The return value
is a list of two elements, the node-handle followed by the
index.

Command [pathName text offset] is the reverse of 
[pathName text index]. Given a node-handle and index of the
type similar to that used by the [pathName tag] commands,
this command returns the corresponding character offset in the 
string returned by [pathName text text] command.
.RE

pathName write continue
.br
pathName write text html-text
.br
pathName write wait
.br
.RS
TODO
.RE

pathName xview
.br
pathName xview moveto fraction
.br
pathName xview scroll number what
.br
.RS
This command is used to query or adjust the horizontal
position of the viewport relative to the document layout.
It is identical to the [pathName xview] command
implemented by the canvas and text widgets.
.RE

pathName yview
.br
pathName yview moveto fraction
.br
pathName yview scroll number what
.br
pathName yview nodeHandle
.br
.RS
This command is used to query or adjust the vertical
position of the viewport relative to the document layout.
It supports a superset of the [pathName yview] interface
implemented by the canvas and text widgets.

As well as the standard interface copied from the canvas 
and text widgets, Tkhtml supports passing a single node-handle
as the only argument to [pathName yview]. In this case 
the viewport is scrolled so that the content generated by
the node nodeHandle is visible. This can be useful for
implementing support for URI fragments.
.RE

.SH "NODE COMMAND"
There are several interfaces by which a script can obtain a "node
handle".  Each node handle is a Tcl command that may be used to
access the document node that it represents. A node handle is valid
from the time it is obtained until the next call to 
[pathName reset]. The node handle may be used to query and
manipulate the document node via the following subcommands:

nodeHandle attribute ??-default default-value? ?attribute? ?new-value??
.br
.RS
If the attribute argument is present, then return the value
of the named html attribute. If the attribute is not defined
for the node, then a copy of the default-value argument is
returned instead. If no \-default option was specified (and
hence there is no default-value argument) and the named
attribute does not exist, an error is raised.

If the new-value argument is present, then set the named
                attribute to the specified new-value.

If no attribute argument is present, return a key-value list
of the defined attributes of the form that can be passed to 
[array set].
.RS

.nf
# Html code for node
<p class="normal" id="second" style="color : red">

# Value returned by [nodeHandle attr]
{class normal id second style {color : red}}

# Value returned by [nodeHandle attr class]
normal
.fi
.RE
.RE

nodeHandle children
.br
.RS
Return a list of node handles for all children of nodeHandle.
The leftmost child node becomes element 0 of the list, the
second leftmost element 1, and so on.
.RE

nodeHandle destroy
.br
.RS
TODO. Experimental.
.RE

nodeHandle dynamic set ?flag?
.br
nodeHandle dynamic clear ?flag?
.br
.RS
Set or clear a dynamic flag on a node. 

The supported values for the flag argument are "active",
"hover", "focus", "link" and "visited". The status of each
dynamic flag determines whether or not the corresponding CSS
dynamic pseudo-classes are considered to match the node. For
example, when the mouse moves over node $N, a script could
invoke:
.RS

.nf
$N dynamic set hover
.fi
.RE
Or possibly, if $PN were the node the mouse hovered over
previously:
.RS

.nf
for {set n $PN} {$n ne ""} {set n [$n parent]} {
        $n dynamic clear hover
}
for {set n $N} {$n ne ""} {set n [$n parent]} {
        $n dynamic set hover
}
.fi
.RE
.RE

nodeHandle insert ?-before node? node-list
.br
.RS
TODO. Experimental.
.RE

nodeHandle override ?value?
.br
.RS
TODO. Experimental.
.RE

nodeHandle parent
.br
.RS
Return the node handle for the node"s parent. If the node
does not have a parent (i.e. it is the document root), then
return an empty string.
.RE

nodeHandle property ?-before|-after? ?property-name?
.br
.RS
TODO.
.RE

nodeHandle remove ?node-list?
.br
.RS
TODO.
.RE

nodeHandle replace ? ?options? newValue?
.br
.RS
This command is used to set and get the name of the
replacement object for the node, if any. If the newValue
argument is present, then this command sets the nodes
replacement object name and returns the new value. If
newValue is not present, then the current value is
returned.

A nodes replacement object may be set to the name of a Tk
window or an empty string. If it is an empty string (the
default and usual case), then the node is rendered normally.
If the node replacement object is set to the name of a Tk
window, then the Tk window is mapped into the widget in place
of any other content (for example to implement form elements or
plugins).

The following options are supported:
.RS

.nf
Option                   Default Value
\--------------------------------------
\-deletecmd    <script>   ""
\-configurecmd <script>   ""
\-stylecmd     <script>   ""
.fi
.RE

When a replacement object is no longer being used by the
widget (e.g. because the node has been deleted or 
[pathName reset] is invoked), the value of the
\-deletecmd option is evaluated as Tcl script. 

If it is not set to an empty string (the default) each time
the nodes CSS properties are recalculated, a serialized
array is appended to the value of the \-configurecmd option
and the result evaluated as a Tcl command. The script
should update the replacement objects appearance where
appropriate to reflect the property values. The format of
the appended argument is {p1 v1 p2 v2 ... pN vN} where the
pX values are property names (i.e. "background-color") and
the vX values are property values (i.e. "#CCCCCC"). The
CSS properties that currently may be present in the array
are listed below. More may be added in the future.
.RS

.nf
background-color    color
font                selected
.fi
.RE

The value of the "font" property, if present in the
serialized array is not set to the value of the
corresponding CSS property. Instead it is set to the name
of a Tk font determined by combining the various
font-related CSS properties. Unless they are set to
"transparent", the two color values are guaranteed to parse
as Tk colors. The "selected" property is either true or
false, depending on whether or not the replaced object is
part of the selection or not. Whether or not an object is
part of the selection is governed by previous calls to the
[pathName select] command.

The \-configurecmd callback is always executed at least once
between the [nodeHandle replace] command and when the
replaced object is mapped into the widget display.
.RE

nodeHandle tag
.br
.RS
Return the name of the Html tag that generated this
document node (i.e. "p" or "link"), or an empty string if
the node is a text node.
.RE

nodeHandle text ?-tokens|-pre?
.br
.RS
If the node is a "text" node, return the string contained
by the node. If the node is not a "text" node, return an
empty string.

TODO: Document \-tokens and \-pre.
.RE

.SH "STYLESHEET LOADING"
Apart from the default stylesheet that is always loaded (see the
description of the \-defaultstyle option above), a script may
configure the widget with extra style information in the form of
CSS stylesheet documents. Complete stylesheet documents (it is not
possible to incrementally parse stylesheets as it is HTML document
files) are passed to the widget using the [pathName style]
command.

As well as any stylesheets specified by the application,
stylesheets may be included in HTML documents by document authors
in several ways: 
.RS
.IP * 2
Embedded in the document itself, using a <style> tag. To
handle this case an application script must register a
"script" type handler for <style> tags using the 
[pathName handler] command. The handler command should
call [pathName style] to configure the widget with the
stylesheet text.
.IP * 2
Linked from the document, using a <link> tag. To handle
this case the application script should register a "node"
type handler for <link> tags.
.IP * 2
Linked from another stylesheet, using the @import
directive. To handle this, an application needs to
configure the widget \-importcommand option.
.RE
.RS

.nf
# Implementations of application callbacks to load
# stylesheets from the various sources enumerated above.
# ".html" is the name of the applications tkhtml widget.
# The variable $document contains an entire HTML document.
# The pseudo-code <LOAD URI CONTENTS> is used to indicate
# code to load and return the content located at $URI.

proc script_handler {tagcontents} {
    incr ::stylecount
    set id "author.[format %.4d $::stylecount]"
    set handler "import_handler $id"
    .html style \-id $id.9999 \-importcmd $handler $tagcontents
}

proc link_handler {node} {
    if {[node attr rel] == "stylesheet"} {
        set URI [node attr href]
        set stylesheet [<LOAD URI CONTENTS>]

        incr ::stylecount
        set id "author.[format %.4d $::stylecount]"
        set handler "import_handler $id"
        .html style \-id $id.9999 \-importcmd $handler $stylesheet
    }
}

proc import_handler {parentid URI} {
    set stylesheet [<LOAD URI CONTENTS>]

    incr ::stylecount
    set id "$parentid.[format %.4d $::stylecount]"
    set handler "import_handler $id"
    .html style \-id $id.9999 \-importcmd $handler $stylesheet
}

 .html handler script style script_handler
 .html handler node link link_handler

set ::stylecount 0

 .html parse \-final $document
.fi
.RE

The complicated part of the example code above is the generation of
stylesheet-ids, the values passed to the \-id option of the 
[.html style] command. Stylesheet-ids are used to determine the
precedence of each stylesheet passed to the widget, and the role it
plays in the CSS cascade algorithm used to assign properties to
document nodes. The first part of each stylesheet-id, which must be
either "user", "author" or "agent", determines the role the
stylesheet plays in the cascade algorithm. In general, author
stylesheets take precedence over user stylesheets which take
precedence over agent stylesheets. An author stylesheet is one
supplied or linked by the author of the document. A user stylesheet
is supplied by the user of the viewing application, possibly by
configuring a preferences dialog or similar. An agent stylesheet is
supplied by the viewing application, for example the default
stylesheet configured using the \-defaultstyle option.

The stylesheet id mechanism is designed so that the cascade can be
correctly implemented even when the various stylesheets are passed
to the widget asynchronously and out of order (as may be the case
if they are being downloaded from a network server or servers).
.RS

.nf
#
# Contents of HTML document
#

<html><head>
    <link rel="stylesheet" href="A.css">
    <style>
        @import uri("B.css")
        @import uri("C.css")
        ... rules ...
    </style>
    <link rel="stylesheet" href="D.css">
 ... remainder of document ...

#
# Contents of B.css
#

@import "E.css"
 ... rules ...
.fi
.RE

In the example above, the stylesheet documents A.css, B.css, C.css,
D.css, E.css and the stylesheet embedded in the <style> tag are all
author stylesheets. CSS states that the relative precedences of the
stylesheets in this case is governed by the following rules:
.RS
.IP * 2
Linked, embedded or imported stylesheets take precedence
over stylesheets linked, embedded or imported earlier in
the same document or stylesheet.
.IP * 2
Rules specified in a stylesheet take precedence over rules
specified in imported stylesheets.
.RE

Applying the above two rules to the example documents indicates
that the order of the stylesheets from least to most important is:
A.css, E.css, B.css, C.css, embedded <stylesheet>, D.css. For the
widget to implement the cascade correctly, the stylesheet-ids
passed to the six [pathName style] commands must sort
lexigraphically in the same order as the stylesheet precedence
determined by the above two rules. The example code above shows one
approach to this. Using the example code, stylesheets would
be associated with stylesheet-ids as follows: 
.RS

.nf
Stylesheet         Stylesheet-id
\-------------------------------
A.css              author.0001.9999
<embedded style>   author.0002.9999
B.css              author.0002.0003.9999
E.css              author.0002.0003.0004.9999
C.css              author.0002.0005.9999
D.css              author.0006.9999
.fi
.RE

Entries are specified in the above table in the order in which the
calls to [html style] would be made. Of course, the example code
fails if 10000 or more individual stylesheet documents are loaded.
More inventive solutions that avoid this kind of limitation are
possible.

Other factors, namely rule specificity and the !IMPORTANT directive
are involved in determining the precedence of individual stylesheet
rules. These are completely encapsulated by the widget, so are not
described here. For complete details of the CSS cascade algorithm,
refer to the CSS and CSS 2 specifications (www.w3.org).

.SH "ORPHAN NODES"