fix: replace HTML_LOWER_CASE regex with Set to prevent false matches on custom elements

The regex could incorrectly match custom element properties (e.g. channelId
matching the `ch` prefix, resulting in `channelid`). Using an explicit Set
ensures only known HTML attributes are lowercased.

Fixes #451

Author: baspinarenes

CHANGELOG.md

@@ -6,6 +6,8 @@
 
 - [#446](https://github.com/preactjs/preact-render-to-string/pull/446) [`b7b288c`](https://github.com/preactjs/preact-render-to-string/commit/b7b288c68ed8c97ed8eb6c26929111debdc03435) Thanks [@JoviDeCroock](https://github.com/JoviDeCroock)! - Fix issues regarding streaming full HTML documents
 
+- Replace `HTML_LOWER_CASE` regex with an explicit `Set` for camelCase HTML attribute name lookup. The regex could incorrectly match custom element properties (e.g. `channelId` matching the `ch` prefix, resulting in `channelid`). Using a `Set` ensures only known HTML attributes are lowercased.
+
 ## 6.6.5
 
 ### Patch Changes

package-lock.json

@@ -666,7 +666,7 @@ function _renderToString(
 								? 'panose-1'
 								: name.replace(/([A-Z])/g, '-$1').toLowerCase();
 					}
-				} else if (HTML_LOWER_CASE.test(name)) {
+				} else if (HTML_LOWER_CASE.has(name)) {
 					name = name.toLowerCase();
 				}
 			}

src/index.js

@@ -4,7 +4,50 @@ export const VOID_ELEMENTS = /^(?:area|base|br|col|embed|hr|img|input|link|meta|
 // oxlint-disable-next-line no-control-regex
 export const UNSAFE_NAME = /[\s\n\\/='"\0<>]/;
 export const NAMESPACE_REPLACE_REGEX = /^(xlink|xmlns|xml)([A-Z])/;
-export const HTML_LOWER_CASE = /^(?:accessK|auto[A-Z]|cell|ch|col|cont|cross|dateT|encT|form[A-Z]|frame|hrefL|inputM|maxL|minL|noV|playsI|popoverT|readO|rowS|src[A-Z]|tabI|useM|item[A-Z])/;
+export const HTML_LOWER_CASE = new Set([
+	'accessKey',
+	'autoCapitalize',
+	'autoComplete',
+	'autoCorrect',
+	'autoFocus',
+	'autoPlay',
+	'cellPadding',
+	'cellSpacing',
+	'charSet',
+	'colSpan',
+	'contentEditable',
+	'contextMenu',
+	'controlsList',
+	'crossOrigin',
+	'dateTime',
+	'encType',
+	'formAction',
+	'formEncType',
+	'formMethod',
+	'formNoValidate',
+	'formTarget',
+	'frameBorder',
+	'hrefLang',
+	'inputMode',
+	'maxLength',
+	'minLength',
+	'noValidate',
+	'playsInline',
+	'popoverTarget',
+	'popoverTargetAction',
+	'readOnly',
+	'rowSpan',
+	'srcDoc',
+	'srcLang',
+	'srcSet',
+	'tabIndex',
+	'useMap',
+	'itemScope',
+	'itemType',
+	'itemID',
+	'itemRef',
+	'itemProp'
+]);
 export const SVG_CAMEL_CASE = /^ac|^ali|arabic|basel|cap|clipPath$|clipRule$|color|dominant|enable|fill|flood|font|glyph[^R]|horiz|image|letter|lighting|marker[^WUH]|overline|panose|pointe|paint|rendering|shape|stop|strikethrough|stroke|text[^L]|transform|underline|unicode|units|^v[^i]|^w|^xH/;
 
 // Boolean DOM properties that translate to enumerated ('true'/'false') attributes

src/lib/util.js

@@ -299,7 +299,7 @@ function _renderToStringPretty(
 							? 'panose-1'
 							: name.replace(/([A-Z])/g, '-$1').toLowerCase();
 				}
-			} else if (HTML_LOWER_CASE.test(name)) {
+			} else if (HTML_LOWER_CASE.has(name)) {
 				name = name.toLowerCase();
 			}