Add Code Standards.

CODING_STANDARDS.md

@@ -0,0 +1,93 @@
+# PHPMarkup coding standards
+
+1. Variable names must be meaningful. One letter variable names must be avoided,
+    except for places where the variable has no real meaning or a trivial
+    meaning (e.g. `for (i=0; i<100; i++) ...`).
+
+    Rule inherited from [PHP](https://github.com/php/php-src/edit/master/CODING_STANDARDS.md).
+
+2. Variable names should be in lowercase. Use underscores to separate between
+    words.
+
+   Good:
+
+    ```php
+    $person = new Person();
+    $person_id = 1;
+    $max_int_value = 2;
+    ```
+
+    Bad:
+
+    ```php
+    $Person = new Person();
+    $personId = 1;
+    $maxIntValue = 2;
+    ```
+
+    Rule inherited from [PHP](https://github.com/php/php-src/edit/master/CODING_STANDARDS.md).
+
+3. Method names follow the *studlyCaps* (also referred to as *bumpy case* or
+    *camel caps*) naming convention, with care taken to minimize the letter
+    count. The initial letter of the name is lowercase, and each letter that
+    starts a new `word` is capitalized:
+
+    Good:
+
+    ```php
+    connect()
+    getData()
+    buildSomeWidget()
+    ```
+
+    Bad:
+
+    ```php
+    get_Data()
+    buildsomewidget()
+    getI()
+    ```
+
+    Rule inherited from [PHP](https://github.com/php/php-src/edit/master/CODING_STANDARDS.md).
+
+4. Class names should be descriptive nouns in *PascalCase* and as short as
+    possible. Each word in the class name should start with a capital letter,
+    without underscore delimiters. The class name should be prefixed with the
+    name of the "parent set" (e.g. the name of the extension) if no namespaces
+    are used. Abbreviations and acronyms as well as initialisms should be
+    avoided wherever possible, unless they are much more widely used than the
+    long form (e.g. HTTP or URL). Abbreviations start with a capital letter
+    followed by lowercase letters, whereas acronyms and initialisms are written
+    according to their standard notation. Usage of acronyms and initialisms is
+    not allowed if they are not widely adopted and recognized as such.
+
+    Good:
+
+    ```php
+    Curl
+    CurlResponse
+    HTTPStatusCode
+    URL
+    BTreeMap // B-tree Map
+    Id // Identifier
+    ID // Identity Document
+    Char // Character
+    Intl // Internationalization
+    Radar // Radio Detecting and Ranging
+    ```
+
+    Bad:
+
+    ```php
+    curl
+    curl_response
+    HttpStatusCode
+    Url
+    BtreeMap
+    ID // Identifier
+    CHAR
+    INTL
+    RADAR // Radio Detecting and Ranging
+    ```
+
+    Rule inherited from [PHP](https://github.com/php/php-src/edit/master/CODING_STANDARDS.md).