Anunderlineisoneormorehorizontallinesimmediatelybelowaportionofwriting.Single,andoccasionallydouble,underliningwasoriginallyusedinhand-writtenortypewrittendocumentstoemphasisetext.Inamanuscripttobetypeset,variousformsofunderliningwereconventionallyusedtoindicatethattextshouldbesetinaspecialtypefacesuchasitalicstoshowemphasis,partofaprocedureknownasmarkup.Withtheadventofwordprocessing,differenttypefacescanbeusedinthemanuscriptdirectly,sothatunderliningisnolongerneededformarkup;butunderliningissometimesusedindocumentsinitsownright.

　　Underlinesaresometimesusedasadiacritic,toindicatethataletterhasadifferentpronunciationtoitsnon-underlinedform.

　　[edit]Usewithcomputers

　　Inwebbrowsers,defaultsettingstypicallydistinguishhyperlinksbyunderliningthem(andusuallychangingtheircolor),butbothusersandwebsitescanchangethesesettingstomakesomeorallhyperlinksappeardifferently(orevenwithoutdistinctionfromnormaltext).

　　TheHTMLspecialinlineelement,denotinginsertedtext,isoftenpresentedasunderlinedtext.HTMLalsohasapresentationalelement,denotingunderlinedtext;thisisdeprecatedinfavouroftheCSSstyle{text-decoration:underline}.Theseelementsmayalsoexistinothermarkuplanguages,suchasMediaWiki.

　　Inplain-text(ASCII)computerfiles,includinge-mailcommunication,whereunderliningisnotpossible,itisoftenindicatedbysurroundingwordswithunderscorecharacters.Forexample,"Youmustusean_emulsion_paintontheceiling".

　　Unicodehasthecombiningdiacritic"combininglowline"atU+0332̲thatresultsinanunderlinewhenruntogether:u̲n̲d̲e̲r̲l̲i̲n̲e̲.Nottobeconfusedisthecombiningmacronbelow.

　　Underline(typicallyredand/orwavy)isoftenusedbyspellcheckers(andgrammarcheckers)todenotemisspelledorotherwiseincorrecttext.

　　Underlinesinnon-Latinscripts

　　InChinese,theunderlineisapunctuationmarkforpropernames(专名号,专名号;pinyin:zhuānmínghào;literally“propernamemark”,usedforpersonalandgeographicnames).ItsmeaningissomewhatakintocapitalizationinEnglishandshouldneverbeusedforemphasis;however,duetotheinfluenceofEnglishcomputing,theunderlineisnowsometimesusedforemphasis.Awavyunderline(书名号,书名号;pinyin:shūmínghào;literally“booktitlemark”)servesasimilarfunction,butmarksnamesofliteraryworksinsteadofpropernames.

　　Inthecaseoftwoormoreadjacentpropernames,eachindividualpropernameisseparatelyunderlined,sothereshouldbeaslightgapbetweentheunderliningofeachpropername.

　　Manuscripts

　　Thefollowingkindsofunderlinesareusedonmanuscriptstoindicatespecialtypefacestobeused.

　　singleunderlineforitalictype

　　doubleunderlineforsmallcaps

　　tripleunderlineforfullcapitalletters(usedamongsmallcapsortochangetextalreadytypedaslowercase)

　　wavyunderlineforboldface

　　en.wikipedia.org/wiki/Underline

　　Whenwritingaboutotherworks,it'shardtodecidewhentounderline(orplaceinitalics)atitleandwhentoplaceitindoublequotations.Notethatsomepublicationshavea"housestyle"thatmustbefollowed.Whenind