tutorial draft

doc/tutorial.md

+# RapidJSON Tutorial
+
+This tutorial introduces Document Object Model(DOM) API of RapidJSON.
+
+As shown in [Usage at a glance](../readme.md#usage-at-a-glance), a JSON text can be parsed into DOM, and then be quried and modfied easily, and finally convert back to JSON text.
+
+## Value
+
+Each JSON value is stored in a type called `Value`. A `Document`, representing the DOM, contains the root of `Value`.
+
+### Querying Value
+
+In this section, we will use excerpt of [`example/tutorial/tutorial.cpp`](../example/tutorial/tutorial.cpp).
+
+Assumes we have a JSON text stored in a C string (`const char* json`):
+```js
+{
+    "hello": "world",
+    "t": true ,
+    "f": false,
+    "n": null,
+    "i": 123,
+    "pi": 3.1416,
+    "a": [1, 2, 3, 4]
+}
+```
+
+Parse it into a `Document`
+```cpp
+#include "rapidjson/document.h"
+
+using namespace rapidjson;
+
+// ...
+Document document;
+document.Parse(json);
+```
+
+The JSON text is now parsed into `document` as a DOM tree.
+
+The root of a conforming JSON should be either an object or an array. In this case, the root is an object with 7 members.
+```cpp
+assert(document.IsObject());
+```
+
+Query whether a `"hello"` member exists in the root object. Since a `Value` can contain different types of value, we may need to verify its type and use suitable API to obtain the value. In this example, `"hello"` member associates with a JSON string.
+```cpp
+assert(document.HasMember("hello"));
+assert(document["hello"].IsString());
+printf("hello = %s\n", document["hello"].GetString());
+```
+
+JSON true/false values are represented as `bool`.
+```cpp
+assert(document["t"].IsBool());
+printf("t = %s\n", document["t"].GetBool() ? "true" : "false");
+```
+
+JSON null can be queryed by `IsNull()`.
+```cpp
+printf("n = %s\n", document["n"].IsNull() ? "null" : "?");
+```
+
+JSON number type represents all numeric values. However, C++ needs more specific type for manipulation.
+
+```cpp
+assert(document["i"].IsNumber());
+
+// In this case, IsUint()/IsInt64()/IsUInt64() also return true.
+assert(document["i"].IsInt());          
+printf("i = %d\n", document["i"].GetInt());
+// Alternative (int)document["i"]
+
+assert(document["pi"].IsNumber());
+assert(document["pi"].IsDouble());
+printf("pi = %g\n", document["pi"].GetDouble());
+```
+
+JSON array contains a number of elements
+```cpp
+// Using a reference for consecutive access is handy and faster.
+const Value& a = document["a"];
+assert(a.IsArray());
+for (SizeType i = 0; i < a.Size(); i++) // Uses SizeType instead of size_t
+        printf("a[%d] = %d\n", i, a[i].GetInt());
+```
+
+Note that, RapidJSON do not automatically converting between JSON types. if a value is a string, it is invalid to call `GetInt()`.  In debug mode it will assert. In release mode, the behavior is undefined.
+
+## Create/Modify Values
+
+## Object
+
+## Array
+
+## String
+
+## Number
+
+## True/False/Null