More strictly describe a runtime type restriction
If the described restriction is not followed the method will eventually
throw (though the error is not always clear). In other docs with
descriptions of conditions that cause errors we use "must".
diff --git a/lib/src/client.dart b/lib/src/client.dart
index 12695e7..c0d475e 100644
--- a/lib/src/client.dart
+++ b/lib/src/client.dart
@@ -44,7 +44,7 @@
/// Sends an HTTP POST request with the given headers and body to the given
/// URL.
///
- /// [body] sets the body of the request. It can be a [String], a [List<int>]
+ /// [body] sets the body of the request. It must be a [String], a [List<int>]
/// or a [Map<String, String>]. If it's a String, it's encoded using
/// [encoding] and used as the body of the request. The content-type of the
/// request will default to "text/plain".
@@ -65,7 +65,7 @@
/// Sends an HTTP PUT request with the given headers and body to the given
/// URL.
///
- /// [body] sets the body of the request. It can be a [String], a [List<int>]
+ /// [body] sets the body of the request. It must be a [String], a [List<int>]
/// or a [Map<String, String>]. If it's a String, it's encoded using
/// [encoding] and used as the body of the request. The content-type of the
/// request will default to "text/plain".
@@ -86,7 +86,7 @@
/// Sends an HTTP PATCH request with the given headers and body to the given
/// URL.
///
- /// [body] sets the body of the request. It can be a [String], a [List<int>]
+ /// [body] sets the body of the request. It must be a [String], a [List<int>]
/// or a [Map<String, String>]. If it's a String, it's encoded using
/// [encoding] and used as the body of the request. The content-type of the
/// request will default to "text/plain".
