Support UTF-8 Table names

Added support for UTF-8 Table names (including
combined character)

src/PhpSpreadsheet/Worksheet/Table.php

@@ -103,10 +103,10 @@ class Table
         ) {
             throw new PhpSpreadsheetException('The table name can\'t be the same as a cell reference');
         }
-        if (!preg_match('/^[A-Z_\\\\]/i', $name)) {
+        if (!preg_match('/^[\p{L}_\\\\]/iu', $name)) {
             throw new PhpSpreadsheetException('The table name must begin a name with a letter, an underscore character (_), or a backslash (\)');
         }
-        if (!preg_match('/^[A-Z_\\\\][A-Z0-9\._]+$/i', $name)) {
+        if (!preg_match('/^[\p{L}_\\\\][\p{L}\p{M}0-9\._]+$/iu', $name)) {
             throw new PhpSpreadsheetException('The table name contains invalid characters');
         }
 

tests/PhpSpreadsheetTests/Worksheet/Table/TableTest.php

@@ -42,6 +42,8 @@ class TableTest extends SetupTeardown
             ['_table_2', '_table_2'],
             ['\table_3', '\table_3'],
             ["	Table_4 \n", 'Table_4'],
+            ['table.5', 'table.5'],
+            ['தமிழ்', 'தமிழ்'], // UTF-8 letters with combined character
         ];
     }
 
@@ -72,6 +74,7 @@ class TableTest extends SetupTeardown
             ['R11C11'],
             ['123'],
             ['=Table'],
+            ['ிக'], // starting with UTF-8 combined character
             [bin2hex(random_bytes(255))], // random string with length greater than 255
         ];
     }