Support 1-3 spaces prefixing a code fence per specification (fixes #107).

lib/shared.js

@@ -141,7 +141,7 @@ function makeTokenCache(params) {
   // Find fenced code by pattern (parser ignores "``` close fence")
   params.lines.forEach(function forLine(line, lineIndex) {
     var metadata = 0;
-    var match = /^(`{3,}|~{3,})/.exec(line);
+    var match = /^[ ]{0,3}(`{3,}|~{3,})/.exec(line);
     var fence = match && match[1];
     if (fence &&
         (!inFence || (fence.substr(0, fenceStart.length) === fenceStart))) {

test/code-blocks-prefixed-by-spaces.json

@@ -0,0 +1,6 @@
+{
+  "default": true,
+  "MD013": {
+    "code_blocks": false
+  }
+}

test/code-blocks-prefixed-by-spaces.md

@@ -0,0 +1,39 @@
+# md013-code-blocks-spaces
+
+Text text text text text text text text text text text text text text text text text text. {MD013}
+
+```text
+Text text text text text text text text text text text text text text text text text text.
+```
+
+ ```text
+ Text text text text text text text text text text text text text text text text text text.
+ ```
+
+  ```text
+  Text text text text text text text text text text text text text text text text text text.
+  ```
+
+   ```text
+   Text text text text text text text text text text text text text text text text text text.
+   ```
+
+    ```text
+    Text text text text text text text text text text text text text text text text text text.
+    ```
+
+Text text text text text text text text text text text text text text text text text text. {MD013}
+
+ ```text
+ Text text text text text text text text text text text text text text text text text text.
+```
+
+   ```text
+ Text text text text text text text text text text text text text text text text text text.
+```
+
+  ```text
+ Text text text text text text text text text text text text text text text text text text.
+ ```
+
+Text text text text text text text text text text text text text text text text text text. {MD013}