add more docs

src/Buffer.ts

@@ -18,10 +18,20 @@ export const CHAR_DATA_WIDTH_INDEX = 2;
 export const CHAR_DATA_CODE_INDEX = 3;
 export const MAX_BUFFER_SIZE = 4294967295; // 2^32 - 1
 
+/**
+ * Null cell - a real empty cell (containing nothing).
+ * Note that code should always be 0 for a null cell as
+ * several test condition of the buffer line rely on this.
+ */
 export const NULL_CELL_CHAR = '';
 export const NULL_CELL_WIDTH = 1;
 export const NULL_CELL_CODE = 0;
 
+/**
+ * Whilespace cell.
+ * This is meant as a replacement for empty cells when needed
+ * during rendering lines to preserve correct aligment.
+ */
 export const WHITESPACE_CELL_CHAR = ' ';
 export const WHITESPACE_CELL_WIDTH = 1;
 export const WHITESPACE_CELL_CODE = 32;