Docs: refine helper program and local grading docs

web/docs/api/01-problem-spec.md

@@ -413,63 +413,6 @@ Executed right before the produced output is validated against the output format
 
 ---
 
-## Problem style config
-
-### `StyleConfig()`
-
-```cpp
-virtual void StyleConfig() {}
-```
-
-Defines the options to enable for problem styles. The following methods are exposed:
-
----
-
-#### `BatchEvaluator()`
-
-```cpp
-void BatchEvaluator();
-```
-
-Declares that the problem uses batch evaluator.
-
-#### `InteractiveEvaluator()`
-
-```cpp
-void InteractiveEvaluator();
-```
-
-Declares that the problem uses interactive evaluator.
-
-#### `CustomScorer()`
-
-```cpp
-void CustomScorer();
-```
-
-Declares that the problem needs a custom scorer.
-
-#### `NoOutput()`
-
-```cpp
-void NoOutput();
-```
-
-Declares that the problem does not need test case output files.
-
-See [Problem styles](../topic-guides/styles) for more details.
-
-**Example**
-
-```cpp
-void StyleConfig() {
-    CustomScorer();
-    NoOutput();
-}
-```
-
----
-
 ## Constraints and subtasks
 
 ### `MultipleTestCasesConstraints()`
@@ -586,6 +529,54 @@ void MultipleTestCasesConfig() {
 
 ---
 
+## Problem style config
+
+### `StyleConfig()`
+
+```cpp
+virtual void StyleConfig() {}
+```
+
+Defines the options to enable for [problem styles](../topic-guides/styles). The following methods are exposed:
+
+---
+
+#### `NoOutput()`
+
+```cpp
+void NoOutput();
+```
+
+Declares that the problem does not need test case output files.
+
+#### `CustomScorer()`
+
+```cpp
+void CustomScorer();
+```
+
+Declares that the problem needs a custom scorer.
+
+#### `InteractiveEvaluator()`
+
+```cpp
+void InteractiveEvaluator();
+```
+
+Declares that the problem uses interactive evaluator.
+
+
+**Example**
+
+```cpp
+void StyleConfig() {
+    CustomScorer();
+    NoOutput();
+}
+```
+
+---
+
 ## Grading config
 
 ### `GradingConfig()`

web/docs/api/05-helper.md

@@ -0,0 +1,128 @@
+# Helper programs
+
+TCFrame's [local grading](../topic-guides/grading) system allows the use of **helper** programs, which includes scorer and communicator programs. This is the format that complies with TCFrame's local grading system. If your grading system expects a different format, please adjust the helper programs before setting up the problem there.
+
+## Scorer
+
+A scorer reads the contestant's output and then outputs the verdict.
+
+|Input||
+|-|-|
+|argv[1]|test case input filename|
+|argv[2]|test case output filename|
+|argv[3]|contestant's output filename|
+
+|Output||
+|-|-|
+|stdout|verdict (see the [format](#verdict-format) in the next section)|
+
+Here is an example scorer which gives AC if the contestant's output differs not more than 1e-9 from the official output.
+
+```cpp title="scorer.cpp"
+#include <bits/stdc++.h>
+using namespace std;
+
+int wa() {
+    cout << "WA" << endl;
+    return 0;
+}
+
+int ac() {
+    cout << "AC" << endl;
+    return 0;
+}
+
+int main(int argc, char* argv[]) {
+    ifstream tc_in(argv[1]);
+    ifstream tc_out(argv[2]);
+    ifstream con_out(argv[3]);
+
+    double tc_ans;
+    tc_out >> tc_ans;
+
+    double con_ans;
+    if (!(con_out >> con_ans)) {
+        return wa();
+    }
+
+    if (abs(tc_ans - con_ans) < 1e-9) {
+        return ac();
+    } else {
+        return wa();
+    }
+}
+```
+
+---
+
+## Communicator
+
+A communicator communicates with the contestant's solution program via stdin/stdout, and then outputs the verdict to stderr.
+
+|Input||
+|-|-|
+|argv[1]|test case input filename|
+|stdin|input from contestant's program|
+
+|Output||
+|-|-|
+|stdout|output to contestant's program|
+|stderr|verdict (see the [format](#verdict-format) in the next section)|
+
+Make sure the communicator flushes after every time it writes output.
+
+Here is an example communicator program in a typical binary search problem.
+
+```cpp title="communicator.cpp"
+#include <bits/stdc++.h>
+using namespace std;
+
+int ac() {
+    cerr << "AC" << endl;
+    return 0;
+}
+
+int wa() {
+    cerr << "WA" << endl;
+    return 0;
+}
+
+int main(int argc, char* argv[]) {
+    ifstream tc_in(argv[1]);
+
+    int N;
+    tc_in >> N;
+
+    int guesses_count = 0;
+
+    while (true) {
+        int guess;
+        cin >> guess;
+
+        guesses_count++;
+
+        if (guesses_count > 10) {
+            return wa();
+        } else if (guess < N) {
+            cout << "TOO_SMALL" << endl;
+        } else if (guess > N) {
+            cout << "TOO_LARGE" << endl;
+        } else {
+            return ac();
+        }
+    }
+}
+```
+
+---
+
+## Verdict format
+
+A scorer and communicator should output the verdict of a test case in the following format:
+
+|Verdict|Meaning|
+|-|-|
+|`AC`|The solution receives full points.|
+|`WA`|The solution receives zero points.|
+|`OK X`|The solution receives partial points, which is `X`.<br/>`X` can be a floating point.<br/>E.g.: `OK 71`|
+|`OK P%`|The solution receives partial points, which is `P`% of the full points.<br/>E.g.:`OK 50%`|