Source: Noto Sans Math

U+21C4 Rightwards Arrow Over Leftwards Arrow

U+21C4 was added in Unicode version 1.1 in 1993. It belongs to the block U+2190 to U+21FF Arrows in the U+0000 to U+FFFF Basic Multilingual Plane.

This character is a Other Symbol and is commonly used, that is, in no specific script.

The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. The word that U+21C4 forms with similar adjacent characters prevents a line break inside it.

The CLDR project calls this character “rightwards arrow over leftwards arrow” for use in screen reading software. It assigns these additional labels, e.g. for search in emoji pickers: arrow, leftwards, over, rightwards.

The Wikipedia has the following information about this codepoint:

An arrow is a graphical symbol, such as ← or →, or a pictogram, used to point or indicate direction. In its simplest form, an arrow is a triangle, chevron, or concave kite, usually affixed to a line segment or rectangle, and in more complex forms a representation of an actual arrow (e.g. ➵ U+27B5). The direction indicated by an arrow is the one along the length of the line or rectangle toward the single pointed end.

Representations

System	Representation
Nº	8644
UTF-8	E2 87 84
UTF-16	21 C4
UTF-32	00 00 21 C4
URL-Quoted	%E2%87%84
HTML hex reference	⇄
Wrong windows-1252 Mojibake	â‡„
HTML named entity	&RightArrowLeftArrow;
HTML named entity	&rightleftarrows;
HTML named entity	&rlarr;
Encoding: EUC_JIS_2004 (hex bytes)	A3 A9
Encoding: EUC_JISX0213 (hex bytes)	A3 A9
Encoding: GB18030 (hex bytes)	81 36 CB 36
Encoding: ISO2022_JP_2004 (hex bytes)	1B 24 28 51 23 29 1B 28 42
Encoding: ISO2022_JP_3 (hex bytes)	1B 24 28 4F 23 29 1B 28 42
Encoding: SHIFT_JIS_2004 (hex bytes)	82 48
Encoding: SHIFT_JISX0213 (hex bytes)	82 48
L^AT_EX	\rightleftarrows
Adobe Glyph List	arrowrightoverleft

Elsewhere

Complete Record

Property	Value
Age (age)	1.1 (1993)
Unicode Name (na)	RIGHTWARDS ARROW OVER LEFTWARDS ARROW
Unicode 1 Name (na1)	RIGHT ARROW OVER LEFT ARROW
Block (blk)	Arrows
General Category (gc)	Other Symbol
Script (sc)	Common
Bidirectional Category (bc)	Other Neutral
Combining Class (ccc)	Not Reordered
Decomposition Type (dt)	none
Decomposition Mapping (dm)	Rightwards Arrow Over Leftwards Arrow
Lowercase (Lower)	✘
Simple Lowercase Mapping (slc)	Rightwards Arrow Over Leftwards Arrow
Lowercase Mapping (lc)	Rightwards Arrow Over Leftwards Arrow
Uppercase (Upper)	✘
Simple Uppercase Mapping (suc)	Rightwards Arrow Over Leftwards Arrow
Uppercase Mapping (uc)	Rightwards Arrow Over Leftwards Arrow
Simple Titlecase Mapping (stc)	Rightwards Arrow Over Leftwards Arrow
Titlecase Mapping (tc)	Rightwards Arrow Over Leftwards Arrow
Case Folding (cf)	Rightwards Arrow Over Leftwards Arrow
ASCII Hex Digit (AHex)	✘
Alphabetic (Alpha)	✘
Bidi Control (Bidi_C)	✘
Bidi Mirrored (Bidi_M)	✘
Composition Exclusion (CE)	✘
Case Ignorable (CI)	✘
Changes When Casefolded (CWCF)	✘
Changes When Casemapped (CWCM)	✘
Changes When NFKC Casefolded (CWKCF)	✘
Changes When Lowercased (CWL)	✘
Changes When Titlecased (CWT)	✘
Changes When Uppercased (CWU)	✘
Cased (Cased)	✘
Full Composition Exclusion (Comp_Ex)	✘
Default Ignorable Code Point (DI)	✘
Dash (Dash)	✘
Deprecated (Dep)	✘
Diacritic (Dia)	✘
Emoji Modifier Base (EBase)	✘
Emoji Component (EComp)	✘
Emoji Modifier (EMod)	✘
Emoji Presentation (EPres)	✘
Emoji (Emoji)	✘
Extender (Ext)	✘
Extended Pictographic (ExtPict)	✘
FC NFKC Closure (FC_NFKC)	Rightwards Arrow Over Leftwards Arrow
Grapheme Cluster Break (GCB)	Any
Grapheme Base (Gr_Base)	✔
Grapheme Extend (Gr_Ext)	✘
Grapheme Link (Gr_Link)	✘
Hex Digit (Hex)	✘
Hyphen (Hyphen)	✘
ID Continue (IDC)	✘
ID Start (IDS)	✘
IDS Binary Operator (IDSB)	✘
IDS Trinary Operator and (IDST)	✘
IDSU (IDSU)	0
ID_Compat_Math_Continue (ID_Compat_Math_Continue)	0
ID_Compat_Math_Start (ID_Compat_Math_Start)	0
Ideographic (Ideo)	✘
InCB (InCB)	None
Indic Mantra Category (InMC)	—
Indic Positional Category (InPC)	NA
Indic Syllabic Category (InSC)	Other
Jamo Short Name (JSN)	—
Join Control (Join_C)	✘
Logical Order Exception (LOE)	✘
Modifier Combining Mark (MCM)	✘
Math (Math)	✔
Noncharacter Code Point (NChar)	✘
NFC Quick Check (NFC_QC)	Yes
NFD Quick Check (NFD_QC)	Yes
NFKC Casefold (NFKC_CF)	Rightwards Arrow Over Leftwards Arrow
NFKC Quick Check (NFKC_QC)	Yes
NFKC_SCF (NFKC_SCF)	Rightwards Arrow Over Leftwards Arrow
NFKD Quick Check (NFKD_QC)	Yes
Other Alphabetic (OAlpha)	✘
Other Default Ignorable Code Point (ODI)	✘
Other Grapheme Extend (OGr_Ext)	✘
Other ID Continue (OIDC)	✘
Other ID Start (OIDS)	✘
Other Lowercase (OLower)	✘
Other Math (OMath)	✔
Other Uppercase (OUpper)	✘
Prepended Concatenation Mark (PCM)	✘
Pattern Syntax (Pat_Syn)	✔
Pattern White Space (Pat_WS)	✘
Quotation Mark (QMark)	✘
Regional Indicator (RI)	✘
Radical (Radical)	✘
Sentence Break (SB)	Other
Soft Dotted (SD)	✘
Sentence Terminal (STerm)	✘
Terminal Punctuation (Term)	✘
Unified Ideograph (UIdeo)	✘
Variation Selector (VS)	✘
Word Break (WB)	Other
White Space (WSpace)	✘
XID Continue (XIDC)	✘
XID Start (XIDS)	✘
Expands On NFC (XO_NFC)	✘
Expands On NFD (XO_NFD)	✘
Expands On NFKC (XO_NFKC)	✘
Expands On NFKD (XO_NFKD)	✘
Bidi Paired Bracket (bpb)	Rightwards Arrow Over Leftwards Arrow
Bidi Paired Bracket Type (bpt)	None
East Asian Width (ea)	neutral
Hangul Syllable Type (hst)	Not Applicable
ISO 10646 Comment (isc)	—
Joining Group (jg)	No_Joining_Group
Joining Type (jt)	Non Joining
Line Break (lb)	Alphabetic
Numeric Type (nt)	none
Numeric Value (nv)	not a number
Simple Case Folding (scf)	Rightwards Arrow Over Leftwards Arrow
Script Extension (scx)
Vertical Orientation (vo)	R