Improve validation message when handle starts with a number

resources/lang/en/validation.php

@@ -156,6 +156,7 @@
 
     'arr_fieldtype' => 'This is invalid.',
     'handle' => 'Must contain only lowercase letters and numbers with underscores as separators.',
+    'handle_starts_with_number' => 'Cannot start with a number.',
     'slug' => 'Must contain only letters and numbers with dashes or underscores as separators.',
     'code_fieldtype_rulers' => 'This is invalid.',
     'composer_package' => 'Must be a valid composer package name (eg. hasselhoff/kung-fury).',

src/Rules/Handle.php

@@ -4,11 +4,16 @@
 
 use Closure;
 use Illuminate\Contracts\Validation\ValidationRule;
+use Illuminate\Support\Str;
 
 class Handle implements ValidationRule
 {
     public function validate(string $attribute, mixed $value, Closure $fail): void
     {
+        if (Str::startsWith($value, range(0, 9))) {
+            $fail('statamic::validation.handle_starts_with_number')->translate();
+        }
+
         if (! preg_match('/^[a-zA-Z][a-zA-Z0-9]*(?:_{0,1}[a-zA-Z0-9])*$/', $value)) {
             $fail('statamic::validation.handle')->translate();
         }

tests/Rules/HandleTest.php

@@ -43,4 +43,10 @@ public function it_outputs_helpful_validation_error()
     {
         $this->assertValidationErrorOutput(trans('statamic::validation.handle'), '_bad_input');
     }
+
+    #[Test]
+    public function it_outputs_helpful_validation_error_when_string_starts_with_number()
+    {
+        $this->assertValidationErrorOutput(trans('statamic::validation.handle_starts_with_number'), '1bad_input');
+    }
 }