doc comment

packages/php-wasm/node/src/test/php.spec.ts

@@ -354,7 +354,7 @@ describe.each(SupportedPHPVersions)('PHP %s', (phpVersion) => {
 			php.mkdir(testDirPath1);
 			php.mkdir(testDirPath2);
 			php.writeFile(testDirPath1 + '/1.txt', '1');
-			php.cp(testDirPath1 + '/1.txt', testDirPath2, { recursive: true });
+			php.cp(testDirPath1 + '/1.txt', testDirPath2);
 			expect(php.fileExists(testDirPath2 + '/1.txt')).toEqual(true);
 			expect(php.readFileAsText(testDirPath2 + '/1.txt')).toEqual('1');
 		});

packages/php-wasm/universal/src/lib/universal-php.ts

@@ -258,7 +258,17 @@ export interface IsomorphicLocalPHP extends RequestHandler {
 
 	/**
 	 * Copies a file or directory in the PHP filesystem to a
-	 * new location.
+	 * new location. The target directory's parent must be a
+	 * valid location in the filesystem prior to copying.
+	 *
+	 * If the target path is a file that already exists,
+	 * it will be overwritten.
+	 *
+	 * If the target path is a directory that already exists,
+	 * the file or directory will be copied into it.
+	 *
+	 * If the target path's parent directory does not exist,
+	 * an error will be thrown.
 	 *
 	 * @param oldPath The file or directory to be copied.
 	 * @param newPath The new, full path to copy the file or directory to.