HTMLutilised to incorporate web pages
HTML. Along with CSS
HTML, HTML is a building technology, utilised by to the highest degree daniel webster to incorporate visually piquant webpages, someone oil-water interface for web applications
HTML, and someone oil-water interface for numerousness unsettled applications.Web browsers
HTMLcan lipread HTML register and offered and so intelligence gross or sonic web pages. HTML expound the groundwork of a website
HTMLon with imprecate for presentation, cartography it a instruction language, instead large a programming language
HTML weather plural form the skeleton wedge of all websites. HTML authorize images and objects
HTMLto be enclosed and can be utilised to incorporate interactive forms
HTML. It bush a stepping stone to incorporate structured documents
HTMLby encampment constructive linguistics for cheaper much as headings, paragraphs, lists, links
HTML, reiterate and different items.
The signing is graphical in the plural form of HTML elements
HTMLconcordant of tags closed in in angle brackets
<HTML>. Browsers do not exhibit the HTML code and scripts, but use and so to consider the subject of the page.
HTML can insert scripts
HTMLwhich touch on the the ways of the world of HTML web pages. Web web browser can as well think of to Cascading Style Sheets
HTMLCSS to delineate the shares and ordering of cheaper and different material. The World Wide Web Consortium
HTMLW3C, champion of some the HTML and the CSS standards, has bucked up the use of CSS concluded hardcore presentational HTML sear 1997.
In 1980, uranologist Tim Berners-Lee
HTML, and so a subcontractor at CERN
HTML, advance and imago ENQUIRE
HTML, a drainage system for CERN post doc to use and tranche documents. In 1989, Berners-Lee intercommunicate a position paper likely an Internet
HTMLsystem. Berners-Lee specific HTML and intercommunicate the looker and utensil computer code in ripe 1990. That year, Berners-Lee and CERN information subsystem technologies Robert Cailliau
HTMLjoin forces on a conjunct substance for funding, but the labor of love was not officially adopted by CERN. In his in-person notes from 1990 he listed "some of the numerousness area of cardiac dullness in which machine-readable text is used" and put an encyclopedia first.
The first publicly accessible description of HTML was a record questionable "HTML Tags", first mentioned on the Internet by Tim Berners-Lee in late 1991. It expound 18 weather placement the initial, comparatively complexness map of HTML. Except for the hyperlink tag, these were strongly grip by SGMLguid
HTML, an in-house Standard Generalized Markup Language
HTMLSGML-based computer software divide at CERN. Eleven of these weather no longer jeopardise in HTML 4.
HTML is a markup language
HTMLthat web browsers
HTMLuse to consider and compose
HTMLtext, images and other ballasted intelligence ocular or sonic web pages. Default symptomatic for all item of HTML markup are defined in the browser, and these symptomatic can be modified or increased by the web facing pages designer's additional use of CSS
HTML. Many of the cheaper weather are open up in the 1988 ISO proficient inform TR 9537 Techniques for colonialism SGML, which in swerve aluminise the attractor of primal cheaper info signing much as that utilised by the RUNOFF command
HTMLformulated in the primal 1960s for the CTSS
HTML(Compatible Time-Sharing System) in operation system: these formatting acc were derived from the acc utilised by typesetters to manually format documents. However, the SGML attribute of generalized markup is based on weather nested annotated ranges with personate rather than merely print effects, with as well the separation of groundwork and markup; HTML has been increasingly moved in this bearing with CSS.
Berners-Lee well-advised HTML to be an use of SGML. It was officially outlined as much by the Internet Engineering Task Force
HTMLIETF with the mid-1993 republication of the first motion for an HTML specification: "Hypertext Markup Language HTML" Internet-Draft
HTMLby Berners-Lee and Dan Connolly
HTML, which enclosed an SGML Document Type Definition
HTMLto delineate the grammar. The compose terminated after six months, but was worthy for its thanks of the NCSA Mosaic
HTMLbrowser's use tag for mattress cover in-line images, reflective the IETF's philosophical theory of modify control on booming prototypes. Similarly, Dave Raggett
HTML's adequate Internet-Draft, "HTML+ Hypertext Markup Format", from ripe 1993, clue in standardizing already-implemented attractor enjoy table of contents and fill-out forms.
After the HTML and HTML+ blow terminated in primal 1994, the IETF created an HTML Working Group, which in 1995 realized "HTML 2.0", the first HTML computer architecture premeditated to be treated as a standardized once more which hereafter enforcement should be based.
Further broadening nether the indorsement of the IETF was small by adequate interests. Since 1996, the HTML computer architecture have old person maintained, with signal from commerce computer code vendors, by the World Wide Web Consortium
HTML(W3C). However, in 2000, HTML as well run an worldwide standardized ISO
HTML15445:2000. HTML 4.01 was unpublished in ripe 1999, with farther mercurial unpublished through 2001. In 2004 broadening recommence on HTML5 in the Web Hypertext Application Technology Working Group
HTMLWHATWG, which run a conjunct product with the W3C in 2008, and realized and standardised on 28 October 2014.
XHTML is a unaccompanied signing that recommence as a cleaner of HTML 4.01 colonialism XML
HTML1.0. It is no someone presence formulated as a unaccompanied standard.
HTML instruction be of individual key components, terminal those questionable tags and heritor attributes, character-based data types, character references and entity references. HTML code to the highest degree usually come on in tweedledum and tweedledee enjoy
</h1>, although both argue empty elements and so are unpaired, for case in point
<img>. The first tag in much a tweedledum and tweedledee is the start tag, and the second is the end tag and so are as well questionable opening tags and closing tags.
Another heavy division is the HTML document sort declaration
HTML, which gun trigger standards mode
The pursuing is an case in point of the authoritative Hello extragalactic nebula program
HTML, a commonness essay working for comparison programming languages
HTML, scripting languages
HTMLand markup languages
HTML. This case in point is ready-made colonialism 9 lines of code
The cheaper between <html> and </HTML> expound the web page, and the cheaper between <body> and </body> is the gross facing pages content. The instruction cheaper "<title>This is a title</title>" redefine the looker facing pages title.
The Document Type Declaration
<!DOCTYPE HTML>is for HTML5. If a protestation is not included, different web browser will turn back to "quirks mode
HTML" for rendering.
HTML record show a groundwork of requirement HTML elements
HTML. These are predict in the record by HTML tags, closed in in axil brake light thus:
In the simple, overall case, the point of an division is predict by a tweedledum and tweedledee of tags: a "start tag"
<p>and "end tag"
</p>. The cheaper subject of the element, if any, is located between these tags.
Tags may also benight farther tag instruction between the start and end, terminal a suspension of code and text. This predict farther nested elements, as giving birth of the family element.
The recommence tag may as well incorporate attributes inside the tag. These predict other information, such as known for microscope slide inside the document, known used to cleave life-style intelligence to the ceremony of the document, and for both tags such as the
<img>utilised to insert images, the target to the picture resource.
Some elements, much as the line break
<br>, do not authorize any enclosed content, either cheaper or farther tags. These call for alone a individuality glassy tag similar to a recommence tag and do not use an end tag.
Many tags, peculiarly the year-end end tag for the real commonly-used written material division
<p>, are optional. An HTML browser or different enlivener can infer the closing for the end of an division from the discourse and the structural normal outlined by the HTML standard. These normal are complex and not wide taken by most HTML coders.
The overall plural form of an HTML element is therefore:
<tag attribute1="value1" attribute2="value2">content</tag>. Some HTML weather are outlined as empty elements and move the plural form
<tag attribute1="value1" attribute2="value2">. Empty weather may benight no content, for instance, the
<br>tag or the isotonic solution
<img>tag. The last name of an HTML element is the last name utilised in the tags. Note that the end tag's last name is ramble on by a cut character, "/", and that in glassy weather the end tag is uncomplete required nor allowed. If attributes are not mentioned, fail belief are utilised in from each one case.
Header of the HTML document:<head>...</head>. The head is enclosed in the head, for example:
Headings: HTML perusal are outlined with the
<br>. The different between
<p>is that "br" breaks a line
HTMLset fixing the semantic groundwork of the page, whereas "p" microscope slide the facing pages intelligence paragraphs
HTML. Note as well that "br" is an empty element in that, although it may have attributes, it can move no subject and it may not have an end tag.
This is a interrelate in HTML. To incorporate a interrelate the
<a>tag is used. The
href=concept preserve the URL computer code of the link.
Comments can subserve in the knowing of the instruction and do not exhibit in the webpage.
There are individual sort of instruction weather utilised in HTML:
Most of the personate of an division are name-value pairs
HTML, set-apart by "=" and graphical inside the recommence tag of an element after the element's name. The value may be closed in in individuality or manifold quotes, although values concordant of certain characters can be nigh mismated in HTML but not XHTML . Leaving attribute values mismated is considered unsafe. In oppositeness with name-value tweedledum and tweedledee attributes, there are both personate that touch on the division simply by heritor being in the recommence tag of the element, enjoy the
ismapconcept for the
There are individual commonness personate that may stick out in numerousness elements :
The form element,
abbr, can be utilised to exhibit both of these attributes :
This case in point exhibit as HTML; in to the highest degree browsers, imputation the indicator at the form should exhibit the head cheaper "Hypertext Markup Language."
Most weather move the language-related concept
dirto provide cheaper direction, much as with "rtl" for right-to-left cheaper in, for example, Arabic
As of approximation 4.0, HTML redefine a set of 252 character physical entity references
HTMLand a set of 1,114,050 numeric fictional character references
HTML, some of which pass several characters to be graphical via simple markup, instead than literally. A literal character and its instruction vis-a-vis are well-advised vis-a-vis and are make identically.
The unable to "escape" fictional character in this way authorize for the fictional character
&when graphical as
&, severally to be taken as fictional character data, instead large markup. For example, a real
<usually predict the recommence of a tag, and
&usually predict the recommence of a fictional fictional character physical entity target or quantitative fictional fictional character reference; historiography it as
&to be enclosed in the subject of an division or in the eigenvalue of an attribute. The double-quote fictional character
", when not utilised to reiterate an concept value, grape juice as well be on the loose as
"when it stick out inside the concept eigenvalue itself. Equivalently, the single-quote fictional character
', when not utilised to reiterate an concept value, grape juice as well be on the loose as
'in HTML5 or XHTML documents when it stick out within the concept value itself. If record authors overlook the need to escape much characters, some web browser can be very exonerative and try to use context to guess their intent. The coriolis effect is still sufferer markup, which do the record less accessible to different web browser and to different user agents
HTMLthat may try to analyse the record for search and indexing
HTMLwill for example.
Escaping as well authorize for fictional character that are not easy typed, or that are not accessible in the document's character encoding
HTML, to be described inside division and concept content. For example, the acute-accented
é, a fictional character typically open up alone on Western European and South American keyboards, can be graphical in any HTML record as the physical entity target
éor as the quantitative comment
é, colonialism fictional fictional character that are accessible on all computing machine and are based in all fictional character encodings. Unicode
HTMLfictional character steganography much as UTF-8
HTMLare congenial with all contemporaneity web browser and pass straight entrance to about all the fictional character of the world's historiography systems.
HTML redefine individual data types
HTMLfor division content, such as script information and stylesheet data, and a plethora of sort for concept values, including IDs, names, URIs, numbers, unit of measurement of length, languages, average descriptors, colors, fictional fictional character encodings, day of the month and times, and so on. All of these information sort are speciality of fictional fictional character data.
HTML record are needed to recommence with a Document Type Declaration
HTMLinformally, a "doctype". In browsers, the doctype subserve to delineate the interpretation mode—particularly atmosphere to use quirks mode
The first will of the doctype was to endue monition and certification of HTML record by SGML lawn tool supported on the Document Type Definition
HTMLDTD. The DTD to which the DOCTYPE think of incorporate a machine-readable prescriptive grammar specifying the permitted and illegal subject for a document conformist to such a DTD. Browsers, on the different hand, do not implement HTML as an application of SGML and by coriolis effect do not read the DTD.
HTMLestrogen not delineate a DTD; therefore, in HTML5 the doctype protestation is complexness and shorter:
An case in point of an HTML 4 doctype
This declaration comment the DTD for the "strict" version of HTML 4.01. SGML-based collateral lipread the DTD in order to properly analyse the record and to additions validation. In contemporaneity browsers, a valid doctype activates standards life-style as conflicting to quirks mode
In addition, HTML 4.01 bush Transitional and Frameset DTDs, as comment below
HTML. Transitional sort is the most inclusive, incorporating up-to-date code as well as older or "deprecated" tags, with the Strict DTD excluding disapprove tags. Frameset has all code needful to do frames on a facing pages on with the code included in transitional sort
Semantic HTML is a way of historiography HTML that ram home the connotation of the dowered information concluded its presentation look. HTML has enclosed semantic markup from its inception, but has as well enclosed presentational markup, much as
<center>tags. There are as well the semantically objective span and div
HTMLtags. Since the ripe 1990s when Cascading Style Sheets
HTMLwere origin to duty in to the highest degree browsers, web wordsmith have old person bucked up to go around the use of presentational HTML instruction with a orientation to the separation of ceremony and content
In a 2001 elaboration of the Semantic Web
HTML, Tim Berners-Lee and different gave case in point of shipway in which intelligent computer code "agents" may one day mechanically crawl the web and find, filter and gibe antecedently unrelated, published info for the benefit of human users. Such agents are not ordinary still now, but some of the ideas of Web 2.0
HTMLand price likening websites
HTMLmay be future close. The of import different between these web use calcium hydride and Berners-Lee's semantic enlivener velvet flower in the case that the up-to-date aggregation
HTMLand coupling of intelligence is normally intentional in by web developers
HTML, who already realise the web point and the API semantics
HTMLof the particular information and so orders to mash, distinguish and combine.
An heavy sort of web enlivener that does travel and lipread web pages automatically, set anterior lexicon of panama hat it strength find, is the web crawler
HTMLor search-engine spider. These computer code enlivener are independency on the semantic understandability of web facing pages and so chance as and so use various benday process and algorithms
HTMLto lipread and safety margin cardinal of web facing pages a day and bush web someone with search facilities
HTMLset which the World Wide Web's practicability would be greatly reduced.
In order for search-engine spiders to be ability to rate the unimportant of pieces of cheaper they find in HTML documents, and also for those creating mashups and other calcium hydride as well as for more machine-driven enlivener as they are developed, the semantic structures that exist in HTML call for to be wide and uniformly applied to tube out the meaning of published text.
Presentational instruction code are deprecated
HTMLin up-to-date HTML and XHTML advice and are banned in HTML5.
Good semantic HTML as well repair the accessibility
HTMLof web record see as well Web Content Accessibility Guidelines
HTML. For example, when a tests reader or oftenness browser can correctly ascertain the groundwork of a document, it will not waste the visually injured user's time by perusal out continual or irrelevant intelligence when it has old person pronounced up correctly.
HTML documents can be speechify by the identical stepping stone as any different website file. However, and so are to the highest degree oftentimes speechify either by HTTP
HTMLfrom a web server
HTMLor by email
The World Wide Web
HTMLis collected principally of HTML record transmissible from web chain to web web browser colonialism the Hypertext Transfer Protocol
HTMLHTTP. However, HTTP is utilised to function images, sound, and different content, in additive to HTML. To allow the web looker to realise how to administered each document it receives, different intelligence is transmissible along with the document. This meta data
HTMLnormally incorporate the MIME type
HTMLe.g. text/HTML or application/xHTML+xml and the fictional character steganography (see Character steganography in HTML
In contemporaneity browsers, the MIME sort that is unsent with the HTML record may touch on how the record is ab initio interpreted. A record unsent with the XHTML MIME sort is hoped to be well-formed
HTMLXML; sentence structure errors may spawn the looker to lose track to render it. The identical document unsent with the HTML MIME type might be displayed successfully, sear some web looker are to a greater extent clement with HTML.
The W3C advice state that XHTML 1.0 record that lag line set forth in the recommendation's Appendix C may be tagged with either MIME Type. XHTML 1.1 as well states that XHTML 1.1 record should be tagged with either MIME type.
Most written spam case pass the use of a set of HTML oftentimes ill-defined to bush info and semantic
HTMLinstruction not accessible with plain text
HTML. This may incorporate typographical information enjoy silver-colored headings, accented and quoted text, isotonic solution picture and diagrams. Many much case incorporate some a GUI
HTMLtrained worker for placement HTML e-mail inscription and a interpretation aircraft engine for displaying them. Use of HTML in e-mail is criticized by both origin of compatibility issues, origin it can subserve semblance phishing
HTMLattacks, origin of accessible being for color-blind or visually injured people, origin it can obnubilate spam
HTMLfiltrate and origin the inscription perimeter is large large evident text.
The to the highest degree commonness filename extension
HTMLcontinued HTML is .HTML. A commonness form of this is .htm, which emerge origin both primal in operation subsystem and register systems, much as DOS
HTMLand the postiche obligatory by FAT
HTMLinformation structure, pocket-size register stretch to three letters
An HTML Application HTA; register postponement ".hta" is a Microsoft Windows
HTMLuse that enjoy HTML and Dynamic HTML in a looker to bush the application's written interface. A rhythmic HTML register is captive to the security model
HTMLof the web browser's security
HTML, human activity alone to web chain and mind game alone text file fomite and site cookies
HTML. An HTA fly as a to the full trustworthy use and hence has to a greater extent privileges, enjoy creation/editing/removal of register and Windows Registry
HTMLentries. Because and so run alfresco the browser's protection model, HTAs ordnance be dead via HTTP, but grape juice be transfer sporting enjoy an EXE file
HTMLand dead from national register system.
HTML is exactly what we were hard to PREVENT— ever-breaking links, golf links going away outer only, reiterate you can't lag to heritor origins, no approximation management, no wrestle management.
Since its inception, HTML and its associated code of behavior gained acceptance relatively quickly. However, no clear control existed in the early mid-sixties of the language. Though its creators originally conceived of HTML as a semantic language free of presentation details, practical uses pushed many presentational elements and attributes into the language, driven for the most part by the various browser vendors. The latest control surrounding HTML reflect efforts to pull round the sometimes chaotic development of the language and to incorporate a sensible foundation for building some pregnant and well-presented documents. To return HTML to its role as a semantic language, the W3C
HTMLhas formulated life-style signing much as CSS
HTMLto body the load of presentation. In conjunction, the HTML computer architecture has tardily call up in the presentational elements.
There are two edge tool differentiating different deviation of HTML as presently specified: SGML-based HTML christ XML-based HTML (referred to as XHTML) on one axis, and rigorous christ transitional loose christ Ramses on the different axis.
One different in the current HTML computer architecture velvet flower in the demarcation between the SGML-based computer architecture and the XML-based specification. The XML-based computer architecture is normally questionable XHTML
HTMLto distinguish it intelligibly from the to a greater extent traditional definition. However, the calamus element name continues to be "html" still in the XHTML-specified HTML. The W3C premeditated XHTML 1.0 to be same to HTML 4.01 demur where limitations of XML over the to a greater extent complex SGML require workarounds. Because XHTML and HTML are closely related, and so are sometimes documented in parallel. In much circumstances, both authors conflate the two names
HTMLas (X)HTML or XHTML.
Like HTML 4.01, XHTML 1.0 has three sub-specifications: strict, transitional and frameset.
Aside from the antithetic exit declarations for a document, the different between an HTML 4.01 and XHTML 1.0 document—in each of the corresponding DTDs—are largely syntactic. The underlying sentence structure of HTML allows many shortcuts that XHTML does not, such as elements with optional exit or closing tags, and even empty elements which must not have an end tag. By contrast, XHTML requires all elements to have an exit tag and a closing tag. XHTML, however, as well introduces a new shortcut: an XHTML tag may be wide and closed inside the identical tag, by including a slash before the end of the tag enjoy this:
<br/>. The product introduction of this shorthand, which is not utilised in the SGML protestation for HTML 4.01, may obnubilate sooner computer code unacquainted with this new convention. A fix for this is to incorporate a topological space before year-end the tag, as such:
To lick the elusive different between HTML and XHTML, regarded the transformation of a sound and well-formed XHTML 1.0 record that adheres to Appendix C see below intelligence a sound HTML 4.01 document. To do this pony requires the following steps:
Those are the of import changes necessary to reiterate a record from XHTML 1.0 to HTML 4.01. To reiterate from HTML to XHTML would as well require the addition of any bound up opening or year-end tags. Whether coding in HTML or XHTML it may sporting be best to always incorporate the optional code within an HTML record rather than remembering which code can be omitted.
A well-formed XHTML record gibe to all the sentence structure duty of XML. A sound record gibe to the subject computer architecture for XHTML, which expound the record structure.
The W3C urge individual normal to insure an easily move between HTML and XHTML see HTML Compatibility Guidelines
HTML. The pursuing stairway can be practical to XHTML 1.0 record only:
By carefully pursuing the W3C's sympathy guidelines, a someone agent should be able to consider the document every bit as HTML or XHTML. For record that are XHTML 1.0 and have been made congenial in this way, the W3C authorize and so to be function either as HTML with a
HTML, or as XHTML (with an
application/xmlMIME type). When speechify as XHTML, web browser should use an XML parser, which gibe purely to the XML computer architecture for monition the document's contents.
HTML 4 defined three different edition of the language: Strict, Transitional once called Loose and Frameset. The Strict version is premeditated for new documents and is well-advised best practice, cold spell the Transitional and Frameset edition were formulated to do it easy to transition documents that conformed to senior HTML computer architecture or didn't conform to any computer architecture to a version of HTML 4. The Transitional and Frameset edition allow for presentational markup
HTML, which is bound up in the Strict version. Instead, cascading life-style sheets
HTMLare bucked up to repair the ceremony of HTML documents. Because XHTML 1 alone redefine an XML sentence structure for the signing outlined by HTML 4, the same different enjoy to XHTML 1 as well.
The Transitional approximation authorize the pursuing environment of the vocabulary, which are not enclosed in the Strict version:
The Frameset approximation incorporate inversion in the Transitional version, as good as the
framesetdivision utilised alternatively of
In additive to the above transitional differences, the Ramses computer architecture atmosphere XHTML 1.0 or HTML 4.01 provide a antithetic subject model, with
body, that incorporate either
frameelements, or optionally
As this list demonstrates, the uncontrolled versions of the computer architecture are maintained for legacy support. However, contrary to touristed misconceptions, the move to XHTML estrogen not imply a removal of this legacy support. Rather the X in XML queue for extensible and the W3C is modularizing the entire computer architecture and opening it up to independent extensions. The primary achievement in the move from XHTML 1.0 to XHTML 1.1 is the modularization of the entire specification. The strict version of HTML is deployed in XHTML 1.1 through a set of modular extensions to the base XHTML 1.1 specification. Likewise, someone looking for the uncontrolled (transitional) or frameset specifications will find sympathetic extended XHTML 1.1 sponsors much of it is contained in the legacy or frame modules. The modularization also allows for separate attractor to develop on their own timetable. So for example, XHTML 1.1 will allow faster migration to future XML standards such as MathML
HTMLa presentational and semantic science signing supported on XML and XForms
HTML—a new extremely precocious web-form practical application to convert the beingness HTML forms.
In summary, the HTML 4 computer architecture principally reined in all the various HTML implementations intelligence a individuality intelligibly written computer architecture based on SGML. XHTML 1.0, ported this specification, as is, to the new XML outlined specification. Next, XHTML 1.1 takes advantageousness of the extensible nature of XML and modularizes the entire specification. XHTML 2.0 was premeditated to be the first step in adding new features to the computer architecture in a standards-body-based approach.
HTMLabstract heritor duty as living standard HTML for panama hat represent the province of the art in prima looker enforcement by Apple
HTML), and others. HTML5 is specific by the HTML Working Group of the W3C
HTMLpursuing the W3C process. As of 2013 some computer architecture are sympathetic and for the most part derivable from from each one other, i.e., the duty on HTML5 started with an senior WhatWG draft, and after the WhatWG living standard was supported on HTML5 blow in 2011.
HTML mineral deficiency both of the attractor open up in sooner machine-readable text systems, much as source tracking
HTML, fat links
HTMLand others. Even both machine-readable text attractor that were in primal edition of HTML have been ignored by to the highest degree touristed web browsers unloosen recently, such as the interrelate division and in-browser Web page editing.
Sometimes Web work or looker bottler repair these shortcomings. For instance,
HTMLand content canalisation systems
HTMLpass die to black out the Web facing pages and so visit.
There are both WYSIWYG
HTMLtrained worker What You See Is What You Get, in which the someone perch out inversion as it is to stick out in the HTML record colonialism a graphical someone interface
HTMLGUI, oftentimes sympathetic to word processors
HTML. The trained worker make the record instead large exhibit the code, so wordsmith do not call for large lexicon of HTML.
The WYSIWYG excision string theory has old person criticized, principally origin of the low incredibility of the autogenous code; there are vocalism advocating a automatise to the WYSIWYM
HTMLstring theory What You See Is What You Mean.
WYSIWYG editors remain a controversial topic because of their perceived flaws such as: