html .pi: A Simple HTML Package for Prolog and CLP Systems
Contents
1. term html_term 3 in general leaves atoms in HTML terms unchanged but translates structures into the corresponding format in HTML applying then html_term 2 recursively to their arguments For example given the following code usr local lib prolog html pl1 main tell html_simple html icon_address clip ClipLogo output_htm1 start title Simple HTML document generated from Prolog image ClipLogo nl heading 1 Simple HTML document This document was produced with the tt html pl library It has facilities for itemize em Generating HTML documents including forms em Parsing input from HTML forms em Producing stand alone forms handlers etc 1 address clip dia fi upm es end l told Loading this code and calling main 0 produces the file html_simple htm1 the contents of which are lt html gt lt title gt Simple HTML document generated from Prolog lt title gt lt img src http www clip dia fi upm es images clip gif gt lt h1 gt Simple HTML document lt h1 gt This document was produced with the lt tt gt html pl lt tt gt library lt br gt It has facilities for lt ul gt lt li gt lt em gt Generating lt em gt HTML documents including forms lt li gt lt em gt Parsing lt em gt input from HTML forms lt li gt lt em gt Producing lt em gt sta2. lt li gt and 3 lt ul gt lt h3 gt lt tt gt enumerate lt tt gt lt h3 gt lt ol gt lt li gt lt b gt red lt b gt lt li gt lt i gt green lt i gt lt li gt lt tt gt blue lt tt gt lt ol gt lt h3 gt lt tt gt description lt tt gt lt h3 gt lt dl gt lt dt gt one lt dt gt lt b gt two lt b gt lt dd gt Description of one and two lt dt gt three lt dd gt Idem of three lt dd gt This lt b gt also lt b gt lt d1 gt lt h3 gt Nice itemize lt h3 gt lt dl gt lt dd gt lt img src http www clip dia fi upm es images redball gif align bottom alt gt pretty lt dd gt lt img src http www clip dia fi upm es images redball gif align bottom alt gt lt b gt fancy lt b gt lt dd gt lt img src http www clip dia fi upm es images redball gif align bottom alt gt nice lt dl gt lt hr gt lt address gt clip dia fi upm es lt address gt lt html1 gt html_simple_form pl A simple file which illustrates the creation of HTML form handlers using the Prolog HTML structures for forms defined in section 4 1 3 It also uses the predicates for producing HTML executa bles explained in section 4 2 and for creating form handlers explained in section 4 3 usr local lib prolog html p1 main html_get_form_input Info 15 html_get_value Info person_name Name response Name Response output_htm1 form_reply start image http www clip dia
3. can be changed through the predicate icon_address 2 See the source file for details html_protect Goal Protects the execution of the goal Goal so that if it ails or gives run time errors suitable HTML output is produced The following section explains the facilities provided by the package for creating form handlers including the parsing of input from HTML forms 4 3 Predicates for Creating Form Handlers An HTML form handler is a special kind of HTML executable that is accessed when a form is submitted I e it is the program designated in the form command The predicates provided to simplify this task are html_form_check Used to ensure that the executable was invoked by an HTML form with a method of POST 12 html_get_form_input Dic Translates input from the form to a dictionary Dic of attribute value pairs It translates empty values to true html_get_value Dic Var Val Gets value Val for attribute Var in dictio nary Dic Does not fail value is gt if not found html_empty_value V Useful to check that a value V from a text area is empty can have spaces newlines and linefeeds default Val Default New Val Useful when the executable can be invoked either directly or by a form to set form defaults If Val is empty because the executable was invoked directly NewVal Default else New Val Val 5 Example Files We have created several example files to illustrate the use of the pred
4. Macro is equivalent to the standard one Translation Care must be taken not to transform a structure into itself this would lead to an infinite loop The package has these two equivalences predefined just to make environ ments more BTFXish html_expansion bf X b X html_expansion it X i X As an example to define structures for the new HTML3 tabbing elements one would define the following clauses html_expansion settab I tabstop id I html_expansion tabto I tab to I 4 2 Predicates for Producing HTML Executables An HTML executable is a standard executable which resides in a directory which is recognized by the corresponding httpd server as containing exe cutables The set of such directories normally includes cgi bin but most httpd servers can be configured so that other directories are also included in this class CGI stands for Common Gateway Interface see http kuhttp cc ukans edu info forms forms intro html for a good introduction of CGI scripts and HTML forms When access to a standard document is requested by a browser the httpd server normally simply returns the contents of the file which is normally in HTML format However if the requested address corresponds to a file in an executable directory then the server first runs the executable and then returns to the requesting browser the output produced by such run which is normally in HTML format or another format which can be handled
5. There exists also a begin Tag struc ture Useful in conjunction with the next structure when including in a document output generated by an existing piece of code e g Tag pre Its use is otherwise discouraged end Tag Translates to the end of an HTML environment of name Tag 4 1 3 Specific Structures for Forms HTML forms are HTML documents or parts of HTML documents which when accessed via a form capable browser Mosaic netscape etc allow the user to perform input through text areas menus radio buttons etc This input is not ultimately handled by the browser Instead forms generally have a submit button When this button is pressed the input provided through the menus text areas etc is sent by the browser to a handler 9 program which can be anywhere on the net The sending browser then waits for a response from that program which comes in the form of a new HTML document See for example http www ncsa uiuc edu SDG Software Mosaic Docs lt fill out forms overview html for details The following HTML terms provide a simple way of producing forms from a Prolog program form Addr Specifies the beginning of a form Addr is the address URL of the program that will handle the form translates to lt form method POST action Addr gt Specifies the end of a form translates to lt form gt checkbox Name State Specifies an input of type checkbox with name Name State on if th
6. by 11 the browser HTML requests to executables are generally information re quests and Logic Programming is a natural choice for developing applications capable of fulfilling such requests Developing a WWW executable in Prolog simply amounts to producing a Prolog program which when executed returns an HTML document The formatting facilities presented in the previous sections can be used for pro viding such a document The Prolog executable can be produced using the usual techniques in Prolog i e through a saved state or by generating a stand alone executable At CLIP we have also developed a simple package for creating Prolog scripts i e files containing source code which simply run when executed in the same way as is usually done for example with shell scripts in UNIX this package will be released soon The Prolog HTML package also contains some simple predicates which somewhat simplify the operation of producing a cgi bin executable save_cgi_bin Name FntryPoint creates an executable corresponding to the current state using a saved state only available in systems which support them The name of the executable will be Name and the entry point when the executable is called will be EntryPoint The executable will also contain an exception handler which produces suitable output via an HTML document if the application fails or gives run time errors see the next predicate The warning icon used in these messages
7. dia fi upm es end compute_reply Mood Potatoes Pizza Coke Passwd0 Text0 Number Colors0 Reply compute_food Potatoes Pizza Coke Food compute_text Text0 Text compute_password Passwd0 Passwd compute_colors Colors0 Colors Reply heading 2 Submitted data gt You are strong Mood gt You want strong Food The password is tt verbatim Passwd gt In the text area you wrote tt verbatim Text gt You chose number tt Number and color s preformatted Colors compute_food no food compute_food on potatoes compute_food on pizza compute_food on coke compute_food on on potatoes and pizza compute_food on on pizza with coke compute_food on on potatoes with coke compute_food on on on potatoes and pizza with coke compute_text T0O T html_empty_value TO gt T Nothing T TO compute_password PO P PO true gt P none P PO compute_colors C0 C co gt C none C CO member X X _ member X _ Xs member X Xs save_cgi_bin html_forms main html_forms html Output the first time the form handler is invoked Content type text html 18 lt html gt lt title gt Sample Form generated from Prolog lt title gt lt hi gt S
8. upm es pub papers ciao_ppcp ps Z M Hermenegildo and K Greene The amp Prolog Sys tem Exploiting Independent And Parallelism New Gener ation Computing 9 3 4 233 257 1991 Available online at ftp clip dia fi upm es pub papers imp ngc final ps Z L Lamport LATEX User s Guide amp Reference Manual Addison Wesley Publishing Company Inc 1986 Online information on TeX and LaTeX is available at http curia ucc ie info TeX menu html 21
9. WW docu ments easily from Prolog including HTML forms It also provides facilities for parsing the input provided by HTML forms independently of whether they have been produced by a Prolog program or not and for producing stand alone form handlers The purpose of this document is to serve as a user s manual as well as a short description of the capabilities of the pack age The package was originally developed for SICStus Prolog 2 and the UPM amp Prolog 5 and CIAO systems 4 3 but has also been adapted to other popular LP CLP systems see the Makefile for details It should be straightforward to adapt it to other Prolog and CLP systems If you find this package useful and develop an application with it we would appreciate if you mention our work by citing the user s manual and or by putting a pointer to its location in our WWW pages http www clip dia fi upm es miscdocs html_p1 html_pl html 2 Getting and Installing html pl The latest version of the Prolog HTML package is available via anonymous ftp from the CLIP ftp server To install simply uncompress and untar the distribution in a convenient directory Then edit the options in Makefile to suit your system In particular copy the files in the images directory to an accessible directory in your server and change ICONDIR http www clip dia fi upm es images to point to this directory if you cannot do that bear in mind that these images will have to travel from Spai
10. ample HTML form lt h1 gt lt hr gt lt h2 gt This is a form lt h2 gt lt form method POST action http www clip dia fi upm es cgi bin html_forms gt Please select mood lt br gt lt input name mood type radio value happy checked gt lt img src http www clip dia fi upm es images smile happy gif align middle gt lt input name mood type radio value sad gt lt img src http www clip dia fi upm es images smile sad gif align middle gt lt p gt What lt strong gt do lt strong gt you want lt br gt lt input name potatoes type checkbox gt Potato e s lt br gt lt input name pizza type checkbox gt Pizza lt br gt lt input name coke type checkbox gt Coke lt hr gt Please write a password lt input type password name pass size 9 maxlength 8 gt lt p gt lt textarea name text rows 5 cols 20 gt Write here something lt textarea gt lt p gt You can choose here lt select name menu1 gt lt option gt one lt option gt lt option selected gt two lt option gt lt option gt three lt option gt lt select gt lt p gt Also here lt select name menu2 multiple gt lt option selected gt red lt option gt lt option selected gt green lt option gt lt option gt blue lt option gt lt select gt lt p gt lt input type submit value Send values gt lt input type reset value Reset values gt lt form gt lt hr gt lt address gt clip dia fi upm es lt addre
11. e checkbox is initially checked translates to an lt input gt element radio Name Value Selected Specifies an input of type radio with name Name several radio buttons which are interlocked must share their name Value is the the value returned by the button if Selected Value the button is initially checked translates to an lt input gt element input Type Atts Specifies an input of type Type with a list of attributes Atts Possible values of Type are text password submit reset translates to an lt input gt element textarea Name Atts Text Specifies an input text area of name Name Text provides the default text to be shown in the area Atts a list of attributes translates to a lt textarea gt environment menu Name Atts Items Specifies a menu of name Name list of attributes Atts and list of options Items The elements of the list Items are marked with the prefix operator to indicate that they are selected translates to a lt select gt environment This is not HTML rather the HTTP protocol requires this content descriptor to be used by form handlers when replying trans lates to Content type text html 10 4 1 4 Extending the Package Along with the obvious solution of changing the source code directly the package has a built in mechanism for extending it by adding clauses to the following predicate html_expansion Macro Translation The new HTML structure
12. edgments This package has been written by Manuel Hermenegildo and Daniel Cabeza using input from L Naish s forms and F Bueno s previous Chat interface Thanks are due to Pedro L pez and other members of the CLIP group for useful feedback on this document and on the package itself References 1 D Cabeza and M Hermenegildo Distributed Concurrent Con straint Execution in the CIAO System In Proccedings of the 1995 COMPULOG NET Workshop on Parallelism and Implementa tion Technologies Utrecht NL September 1995 Available online at ftp clip dia fi upm es pub papers ciao dis impl parimp ps Z 2 M Carlsson Sicstus Prolog User s Manual P O Box 1263 S 16313 Spanga Sweden February 1988 Available online at http www sics se ps sicstus sicstus_toc html 20 3 M Hermenegildo F Bueno M Garcia de la Banda and G Puebla The CIAO Multi Dialect Compiler and System An Experimenta tion Workbench for Future C LP Systems In Proccedings of the ILPS 95 Workshop on Visions for the Future of Logic Program ming Portland Oregon USA December 1995 Available online at ftp clip dia fi upm es pub papers ciao report ilps95ws_final ps Z M Hermenegildo and the CLIP group Some Methodological Issues in the Design of CIAO A Generic Parallel Concurrent Constraint Sys tem In Principles and Practice of Constraint Programming LNCS 874 pages 123 133 Springer Verlag May 1994 Available online at ftp clip dia fi
13. en tt blue heading 3 tt description description one b two Description of one and two three Idem of three This b also heading 3 Nice itemize nice_itemize pretty bf fancy nice address clip dia fi upm es end told html_demo html Output from the above code lt html gt lt This document was generated from Prolog gt lt title gt Sample HTML document generated from Prolog lt title gt lt hi gt Sample HTML document lt h1 gt lt hr gt lt h2 gt Miscellaneous lt h2 gt This is a lt a href label gt lt i gt reference lt i gt lt a gt to lt b gt another lt i gt point lt i gt lt b gt in this document lt p gt Let s be lt img src http www clip dia fi upm es images smile happy gif alt gt lt pre gt These lines are lt b gt preformatted lt b gt See lt pre gt We have left here a lt strong gt free lt strong gt variable 14 lt b gt Warning free variable lt b gt lt p gt This is in verbatim lt samp gt amp 1t NOTE amp gt write amp quot kamp amp amp quot to insert an amp amp lt samp gt lt br gt But this is not lt samp gt lt NOTE gt write Xamp to insert an amp lt samp gt lt p gt lt a name label gt This is the point referenced lt i gt above lt i gt lt a gt lt h2 gt Lists lt h2 gt lt h3 gt lt tt gt itemize lt tt gt lt h3 gt lt ul gt lt li gt one lt li gt two
14. fi upm es images clip gif nl heading 2 Toy Address Server Response form http www clip dia fi upm es cgi bin html_simple_form gt Click here enter name and press return input text mame person_name size 20 end_form end response Name html_empty_value Name response Name Available info on bf Name Info info Name Info response Name No available info on bf Name info clip 341 336 7448 info manuel 341 336 7435 info daniel 341 336 7448 save_cgi_bin html_simple_form main html_simple_form html Output the first time the form handler is invoked Content type text html lt html gt lt img src http www clip dia fi upm es images clip gif gt lt h2 gt Toy Address Server lt h2 gt lt hr gt lt form method POST action http www clip dia fi upm es cgi bin html_simple_form gt Click here enter name and press return lt br gt lt input type text name person_name size 20 gt lt form gt lt html1 gt html_simple_form The executable produced by html_simple_form pl You can try it out at http www clip dia fi upm es cgi bin html_simple_form html_forms pl A more involved example of form handling illustrating more uses of the Prolog HTML structures for forms defined in section 4 1 3 16 usr local lib prolog html p1 main html_get_form_input Info html_
15. get_value Info mood Mood0 html_get_value Info potatoes Potatoes html_get_value Info pizza Pizza html_get_value Info coke Coke html_get_value Info pass Password html_get_value Info text Text html_get_value Info menui Number findall Color member menu2 Color Info Colors compute_reply Mood0 Potatoes Pizza Coke Password Text Number Colors Reply default Mood0 happy Mood output_htm1 form_reply start title Sample Form generated from Prolog heading 1 Sample HTML form Reply heading 2 This is a form form http www clip dia fi upm es cgi bin html_forms Please select mood radio mood happy Mood nl image http www clip dia fi upm es images smile happy gif align middle nl radio mood sad Mood nl image http www clip dia fi upm es images smile sad gif align middle What strong do you want checkbox potatoes Potatoes Potato e s checkbox pizza Pizza Pizza checkbox coke Coke Coke gt Please write a password nl input password name pass size 9 maxlength 8 textarea text rows 5 cols 20 Write here something gt You can choose here menu menui one two three Also here menu menu2 multiple red green blue input submit value Send values n1 input reset value Reset values end_form 17 address clip
16. html pl A Simple HTML Package for Prolog and CLP Systems Description and User s Manual Version 96 1 1 D Cabeza M Hermenegildo 15 Mar 1996 Abstract We describe a simple public domain HTML package for LP CLP systems The package allows generating HTML documents easily from LP CLP systems including HTML forms It also provides facilities for parsing the input provided by HTML forms as well as for creating standalone form handlers The purpose of this document is to serve as a user s manual as well as a short description of the capabilities of the package The package was originally developed for SICStus Prolog and the UPM amp Prolog CIAO systems but has been adapted to a number of popular LP CLP systems The document is also a WWW HTML primer containing suffi cient information for developing medium complexity WWW applica tions in Prolog and other LP and CLP languages 1 Introduction Prolog and its constraint based extensions are excellent tools for developing knowledge based applications It is often useful to interface such applica Computer Science Department Technical University of Madrid UPM Spain dcabeza fi upm es herme fi upm es tions to one of the main on line information exchange forums the World Wide Web WWW This Prolog HTML package aims at providing a set of library procedures which should be useful in this process The package allows generating documents in HTML format the native format of W
17. icates provided by the package and to demonstrate its capabilities For each exam ple we list first the Prolog code p1 and then its output htm1 html_simple pl The code shown in section 4 1 html_simple html Shown in the same place html_demo pl A file that illustrates the creation of HTML pages using the specific Prolog HTML structures defined in section 4 1 2 usr local lib prolog html pl main tell html_demo html output_htm1 start nl comment This document was generated from Prolog title Sample HTML document generated from Prolog heading 1 Sample HTML document heading 2 Miscellaneous This is a ref label it reference to nl bf another it point in this document Let s be nl image http www clip dia fi upm es images smile happy gif alt 13 349 preformatted These lines are b preformatted See We have left here a strong free variable n1 X gt This is in verbatim nl samp verbatim lt NOTE gt write amp amp to insert an amp But this is not samp lt NOTE gt write Xamp to insert an amp label label This is the point referenced it above heading 2 Lists heading 3 tt itemize itemize one two and 3 heading 3 tt enumerate enumerate b red i gre
18. istribution is for amp Prolog CIAO change Makefile options and run make to make a version for your system doc Directory containing the documentation html_pl tex This manual in TRX format html_pl ps This manual in postscript format html_pl html_pl html This manual in html format Needs also the other files in this directory examples Directory containing examples images Directory containing standard images used in the package 4 Using the Package The package comprises three basic building blocks e Facilities for generating HTML documents including forms e Facilities for parsing input from HTML forms e Facilities for producing stand alone form handlers The functionality and predicates of each of these blocks are described in the following sections 4 1 Predicates for Generating HTML Documents output htm1 F Accepts in F an HTML term or a list of HTML terms and sends to the standard output the text which is the rendering of the term s in HTML format html_term F L 7T Accepts in F an HTML term and produces in L a list of atoms which are the rendering of the term in HTML format T is the tail of this list and is usually Used by output_htm1 2 An HTML term is a Prolog term in which certain atoms and structures represent special functionality at the HTML level It can be recursively a list of HTML terms The following are legal HTML terms hello hello world This is an em HTML
19. le almost any HTML construction can be represented with these structures but for the sake of simplifying HTML creation more spe cific structures were designed 2A notable exception are comments 4 1 2 Specific Structures Most of the names of the structures listed here have been fashioned after their ETEX 6 equivalent New structures can be defined by means of the html_expansion 2 predicate see section 4 1 4 Note that these structures take priority over the above ones Used at the beginning of a document translates to lt html gt Used at the end of a document translates to lt html gt Produces a horizontal rule translates to lt hr gt Produces a line break translates to lt br gt Produces a paragraph break translates to lt p gt comment Comment Used to insert an HTML comment translates to lt Comment gt title Title Used to give a title to a document translates to a lt title gt environment image Addr Used to include an image of address URL Addr translates to an lt img gt element image URL Atts Idem with the list of attributes Atts ref Addr Text Produces a hypertext link Addr is the URL of the refer enced resource Text is the text of the reference translates to lt a href Addr gt Text lt a gt label Label Text Labels Text as a target destination with label Label translates to lt a name Label gt Text lt a gt heading N Tex
20. n Europe Also if you will be generat ing cgi bin executables as explained in section 4 2 only available in some systems change CGIBINDIR usr local etc httpd cgi bin to point to a cgi bin type directory where you have write access Finally change SYSTEM to the Prolog system you will be using if your system is not lftp clip dia fi upm es pub software listed perhaps you can make a compatibility file c_ p1 for it providing the necessary support predicates If you do so please send us the changes Now run make html p1 If your OS does not have make then manually produce html pl from html0 pl and the appropriate c_ pl compatibility file changing lt ICONDIR gt and lt CGIBINDIR gt in the code to the correct values Versions of this manual in dvi ps and html formats are pro vided in the distribution in the doc directory The latest version of this manual can be accessed on line from http www clip dia fi upm es miscdocs html_pl html_pl html 3 Contents of the Distribution README COPYING LIB Read these files before using the package CHANGES History of the changes between versions Makefile Makefile for producing html pl Must be edited to suit your system c_system pl Compatibility file for system system html0 pl Main source code from which html pl is made by make html pl This is the main library file which should be loaded into the appli cation The default version in the d
21. nd alone forms handlers lt li gt etc lt ul gt lt hr gt lt address gt clip dia fi upm es lt address gt lt html gt Visualizing this file with a WWW browser produces output similar to figure 1 the best thing is to try it out with your favorite browser As was shown with the previous example HTML terms may contain logic variables provided they are instantiated before the term is translated or out put This allows creating documents piecemeal backpatching of references in documents etc Simple HTML document This document was produced with the html p1 library It has facilities for e Generating HTML documents including forms e Parsing input from HTML forms e Producing stand alone forms handlers e etc clip dia fi upm es Figure 1 Possible visualization of html_simple html In the following sections we list the meaning of the various Prolog struc tures that represent special functionality at the HTML level Any atom not included here is assumed to be normal text and will be passed through to the HTML document These sections are included for reference but in any case the source file is clear enough perhaps more than this description You can also examine section 5 to see examples 4 1 1 General Structures Basically HTML has two kinds of components HTML elements and HTML environments An HTML element has the form lt NAME Attributes gt were NAME is the name of the element and Attributes is a
22. possibly empty sequence of attributes each of them being either an attribute name or an attribute assignment as name Value An HTML environment has the form lt NAME Attributes gt Text lt NAME gt were NAME is the name of the environment an Attributes has the same form as before The general Prolog structures that represent these two HTML construc tions are This is a binary operator Represents an HTML element of name Name and attributes Atts were Atts is a possibly empty list of attributes each of them being either an atom or an structure name value For example the term img src images map gif alt A map ismap is translated into the HTML source lt img src images map gif alt A map ismap gt Note that HTML is not case sensitive so we can use lower case atoms name Text This is a term with functor name 1 and argument Text Rep resents an HTML environment of name name and included text Text For example the term address clip dia fi upm es is translated into the HTML source lt address gt clip dia fi upm es lt address gt name Atts Text This is a term with functor name 2 and arguments Atts and Text Represents an HTML environment of name name attributes Atts and included text Text For example the term a href http www clip dia fi upm es Clip home represents the HTML source lt a href http www clip dia fi upm es gt Clip home lt a gt In princip
23. ss gt lt html gt html_forms The executable produced by html_forms pl You can try it out at http www clip dia fi upm es cgi bin html_forms Additionally you can try out webchat a geographical database server with natural language interface good old Chat starting from http www clip dia fi upm es miscdocs webchat_info html 6 Coming soon The HTML package as it is right now allows producing documents and developing information servers However it would also be useful to be able 19 to directly access the net from a Prolog application and through a transla tion from HTML to Prolog terms read remote pages and manipulate their contents for example to perform an intelligent keyword analysis of the text within or to find pointers within the document and in turn follow them We are working on adding the following features to support this task e Support for the HTTP protocol through builtins e A reversible grammar that can also parse HTML documents and turn them into Prolog terms e Integration with a Concurrency Distribution package The next release will hopefully include these features We are also working on a release of our Prolog Scripts and Concurency Distribution packages which allow writing executable LP CLP scripts and concurrent ex ecution access to remote code active objects etc 1 with standard LP CLP systems Please send any comments bugs suggestions to clip dia fi upm es 7 Acknowl
24. t Produces a heading of level N 1 lt N lt 6 Text is the text to be used as heading translates to a lt hN gt environment itemize Items Produces a list of bulleted items Items is a list of corre sponding HTML terms translates to a lt ul gt environment nice_itemize Items Same as above but uses nicer bullets The bullet used can be changed through the predicate icon_address 2 See the source file for details enumerate Items Produces a list of numbered items Items is a list of corresponding HTML terms translates to an lt ol gt environment description Defs Produces a list of defined items Defs is a list whose elements are definitions each of them being a Prolog sequence com posed by 2 operators The last element of the sequence is the definition the other if any are the defined terms translates to an lt dl gt environment Section 5 shows an example that should clarify this point preformatted Text Used to include preformatted text Text is a list of HTML terms each element of the list being a line of the resulting document translates to a lt pre gt environment verbatim Text Used to include text verbatim special HTML characters lt gt amp are translated into its quoted HTML equivalent Used to include a newline in the HTML source just to improve human readability It translates to the start of an HTML environment of name Tag and attributes Atts
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