XML / Style Files

XML Files

All HTML / XML files are run through the lonxml handler before being served to a user. This allows us to rewrite many portion of a document and to support serverside tags. There are 2 ways to add new tags to the xml parsing engine, either through LON-CAPA style files or by writing Perl tag handlers for the desired tags.

Global Variables

• $Apache::lonxml::debug - debugging control
• @Apache::lonxml::pwd - path to the directory containing the file currently being processed
• @Apache::lonxml::outputstack
  $Apache::lonxml::redirection - these two are used for capturing a subset of the output for later processing, don't touch them directly use &startredirection and &endredirection
• $Apache::lonxml::import - controls whether the <import> tag actually does anything
• @Apache::lonxml::extlinks - a list of URLs that the user is allowed to look at because of the current resource (images, and links)
• $Apache::lonxml::metamode - some output is turned off, the meta target wants a specific subset, use <output> to guarentee that the catianed data will be in the parsing output
• $Apache::lonxml::evaluate - controls whether run::evaluate actually derefences variable references
• %Apache::lonxml::insertlist - data structure for edit mode, determines what tags can go into what other tags
• @Apache::lonxml::namespace - stores the list of tag namespaces used in the insertlist.tab file that are currently active, used only in edit mode.
• $Apache::lonxml::registered - set to 1 once the remote has been updated to know what resource we are looking at.
• $Apache::lonxml::request - current Apache request object, or undef
• $Apache::lonxml::curdepth - current depth of the overall parse depth. Will be a string like: 2_3_1 (first tag in the third second level tag in the second toplevel tag). It gets set by callsub, and can be used in Perl tag implementations. It relies upon the internal globals: @Apache::lonxml::depthcounter, $Apache::lonxml::depth, $Apache::lonxml::olddepth
• $Apache::lonxml::prevent_entity_encode - By default the xmlparser will try to rencode any 8-bit characters into HTML Entity Codes, If this is set to a true value it will be prevented.
• $Apache::lonxml::errorcount - keeps count of the number of errors generated in a parse
• $Apache::lonxml::warningcount - keeps count of the number of errors generated in a parse
• $Apache::lonxml::counter
  $Apache::lonxml::counter_changed - a counter used to keep track of the number of questions asked, used currently to track bubble numbers, Initialized off of $ENV{'form.counter'}, and writes this value to the environment if counter_changed is true, should use the &increment_counter() function to increment this value.
• $Apache::lonxml::default_homework_loaded - a boolean on wherethe the default_homework.lcpm file has been loaded into the Safe Space, the function &Apache::lonxml::default_homework_load()

In common usage, $Apache::lonxml::prevent_entity_encode, $Apache::lonxml::evaluate, $Apache::lonxml::metamode, $Apache::lonxml::import, should never be set to a value directly, but rather incremented when you want the effect on, and decremented when you want the effect off.

Notable Perl subroutines

If not specified these functions are in Apache::lonxml

• xmlparse - see the XMLPARSE figure - also not callable from inside a tag, if one needs to restart parsing, either create add a new LCParser to the parser stack parser using the newparser function, or call inner_xmlparser, see the xmlparse function in scripttag.pm
• recurse - acts just like xmlparse, except it doesn't do the style definition check it always calls callsub
• callsub - callsub looks if a perl subroutine is defined for the current tag and calls. Otherwise it just returns the tag as it was read in. It also will throw on a default editing interface unless the tag has a defined subroutine that either returns something or requests that call sub not add the editing interface.
• afterburn - called on the output of xmlparse, it can add highlights, anchors, and links to regular expersion matches to the output.
• register_insert - builds the %Apache::lonxml::insertlist structure of what tags can have what other tags inside.
• whichuser - returns a list of $symb, $courseid, $domain, $name that is correct for calls to lonnet functions for this setup. Uses form.grade_ parameters, if the user is allowed to mgr in the course
• setup_globals - initializes all lonxml globals when xmlparse is called. If you intend to create a new target you will likely need to tweak how the globals are setup upon start up.
• init_safespace - creates Holes to external functions, creates some global variables, and set the permitted operators of the global Safespace intepreter.

Functions Tag Handlers can use

If not specified these functions are in Apache::lonxml

• debug - a function to call to printout debugging messages. Will only print when Apache::lonxml::debug is set to 1
• warning - a function to use for warning messages. The message will appear at the top of a resource when it is viewed in construction space only.
• error - a function to use for error messages. The message will appear at the top of a resource when it is viewed in construction space, and will message the resource author and course instructor, while informing the student that an error has occured otherwise.
• get_all_text - 2 args, tag to look for (need to use /tag to look for an end tag) and a HTML::TokeParser reference, it will repedelyt get text from the TokeParser until the requested tag is found. It will return all of the document it pulled form the TokeParser. (See Apache::scripttag::start_script for an example of usage.)
• get_param - 4 arguments, first is a scaler sting of the argument needed, second is a reference to the parser arguments stack, third is a reference to the Safe space, and fourth is an optional "context" value. This subroutine allows a tag to get a tag argument, after being interpolated inside the Safe space. This should be used if the tag might use a safe space variable reference for the tag argument. (See Apache::scripttag::start_script for an example.) This version only handles scalar variables.
• get_param_var - 4 arguments, first is a scaler sting of the argument needed, second is a reference to the parser arguments stack, third is a reference to the Safe space, and fourth is an optional "context" value. This subroutine allows a tag to get a tag argument, after being interpolated inside the Safe space. This should be used if the tag might use a safe space variable reference for the tag argument. (See Apache::scripttag::start_script for an example.) This version can handle list or hash variables properly.
• description - 1 argument, the token object. This will return the textual decription of the current tag from the insertlist.tab file.
• whichuser - 0 arguments. This will take a look at the current environment setting and return the current $symb, $courseid, $udom, $uname. You should always use this function if you want to determine who the current user is. (Since a instructor might be trying to view a students version of a resource.)
• inner_xmlparse - 6 arguments, the target, an array pointer to the current stack of tags, and array pointer to the current stack of tag arguments, an array pointer to the current stack of LCParser's, a pointer to the current Safe space, a pointer to the hash of current style definitions
• newparser - 3 args, first is a reference to the parser stack, second should be a reference to a string scaler containg the text the newparser should run over, third should be a scaler of the directory path the file the parser is parsing was in. (See Apache::scripttag::start_import for an example.)
• register - should be called in a file's BEGIN block. 2 arguments, a scaler string, and a list of strings. This allows a file to register what tags it handles, and what the namespace of those tags are. Example:

  sub BEGIN {
    &Apache::lonxml::register('Apache::scripttag',('script','display'));
  }
  

  Would tell xmlparse that in Apache::scripttag it can find handlers for <script> and <display>, if one regsiters a tag that was already registered the previous one is remembered and will be restored on a deregister.
• deregister - used to remove a previously registered tag implementation. It will restore the previous registration if there was one.
• startredirection - used when a tag wants to save a portion of the document for its end tag to use, but wants the intervening document to be normally processed. (See Apache::scripttag::start_window for an example.)
• endredirection - used to stop preventing xmlparse from hiding output. The return value is everthing that xmlparse has processed since the corresponding startredirection. (See Apache::scripttag::end_window for an example.)
• Apache::run::evaluate - 3 args, first a string, second a reference to the Safe space, 3 a string to be evaluated before the first arg. This subroutine will do variable interpolation and simple function interpolations on the first argument. (See Apache::lonxml::inner_xmlparse for an example.)
• Apache::run::run - 2 args, first a string, second a reference to the Safe space. This handles passing the passed string into the Safe space for evaluation and then returns the result. (See Apache::scripttag::start_script for an example.)

Style Files

Style File specific tags

• <definetag> - 2 arguments, name name of new tag being defined, if proceeded with a / defining an end tag, required; parms parameters of the new tag, the value of these parameters can be accesed by $parametername.
• <render> - define what the new tag does for a non meta target
• <meta> - define what the new tag does for a meta target
• <tex> / <web> / <latexsource> - define what a new tag does for a specific no meta target, all data inside a <render> is render to all targets except when surrounded by a specific target tags.

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