Double-Struck Capital H HTML entity &Hopf;

&Hopf; is the HTML entity for Double-Struck Capital H ℍ (U+210D). Copy ℍ, ℍ and the CSS, JavaScript, Python and URL escapes.

Entity: &Hopf;
Also written: &quaternions;
Code point: U+210D
Unicode name: DOUBLE-STRUCK CAPITAL H
Block: Letterlike Symbols
Category: Uppercase letter (Lu)
Since: Unicode 1.1
Defined in: HTML5

Codes to copy

HTML named	`&Hopf;`Works in HTML; in XML only & < > " ' are predefined.
HTML decimal	`ℍ`Works in HTML and XML.
HTML hex	`ℍ`Works in HTML and XML.
CSS	`content: "\210D";`In a stylesheet, for ::before and ::after.
JavaScript	`"\u210D"`Also valid in JSON.
Python	`"\u210d"`Python 3 string literal.
Python by name	`"\N{DOUBLE-STRUCK CAPITAL H}"`Readable alternative using the Unicode name.
URL	`%E2%84%8D`Percent-encoded UTF-8 bytes, for a path or query value.
UTF-8 bytes	`E2 84 8D`3 bytes.
UTF-16	`210D`1 code unit, which is what JavaScript length counts.

When to use it

&Hopf; writes U+210D (Double-Struck Capital H), a capital letter from the Unicode Letterlike Symbols block, encoded since Unicode 1.1. These characters exist mostly for compatibility with older character sets; for anything beyond simple cases, <sup>, <sub> or MathML give more control.

The name comes from the HTML5 list (much of it shared with MathML), so it works in every current browser but not in XML or XHTML served as XML, where the numeric reference is the safe choice.

More letterlike symbols, numbers and fractions

All letterlike symbols, numbers and fractions · Every HTML entity · Encode or decode text

Source: the WHATWG HTML Standard list of named character references and the Unicode Character Database (Unicode 18.0).