Clarify parsing passes.

MEMBERS.md

@@ -15,18 +15,36 @@ Symlinks to the member files serve as human-readable aliases.
 The implementation handles situation when the human-readable name is
 the member file and the symlink is the four-digit member id.
 
-Member File Parsing
+Member File Parsing - Passes 0 and 1
--------------------
+------------------------------------
 
 Member files are read line-by-line.
 
+### Pass 0
+
 Comments start with the ```#``` character and continue until the end
 of particular line.
 
 Comments are stripped from each line before parsing. The same applies
 to leading and trailing whitespace after stripping comments.
 
-Each line should contain a
+### Pass 1
+
+Lines are processed as they are returned from pass 0.
+
+Empty lines are skipped.
+
+Lines without any whitespace are interned as symbols and error is
+recorded as there is only the key and no value associated with it.
+
+Each key/value pair must begin with key token composed of
+non-whitespace characters before the first whitespace. This token is
+interned as symbol upon parsing the line. The remainder of the line is
+stripped of leading whitespace and stored as a string representing the
+value for the key.
+
+The result of parsing is a list of parsed records containing key,
+value and line number for further processing.
 
 Member File Grammar
 -------------------