Syntax rules for consistent message definition

These rules apply to the syntax of messages as they appear in the message library (Figure 1):

The message ID must begin in column 1 of the first line, and the long message must begin in column 1 of the second line. For readability, one or more blank lines can separate the two-line message specifications within the member.
Comments can precede or follow a two-line message specified within a member. A comment begins with the characters /* starting in column one.
In the first line, the fields must be separated by at least one blank. One or more blanks can optionally occur on either side of an equal sign (=).
The short message, if specified, and the long message must each be enclosed in single quotes ('). If the short message is omitted, the enclosing single quotes are also omitted.
Within the short or long message text, any non-alphanumeric character can terminate a variable name. For example:
```
'Enter &X, &Y, or &Z'
```
where a comma terminates the variable names X and Y. The name Z is delimited by the single quote that marks the end of the message.
A period (.) at the end of a variable name has a special meaning. It causes concatenation with the character string following the variable. For example, if the value of variable V is ABC, then:
```
'&V.DEF' yields 'ABCDEF'
```
A single ampersand followed by a blank is interpreted as a literal ampersand character, not the beginning of a substitutable variable. An ampersand followed by a nonblank is interpreted as the beginning of a substitutable variable.
A double ampersand can be used to produce a character string starting with an ampersand. The double character rule also applies to single quotes within the delimiting single quotes required for the short and long message text, and to a period, if it immediately follows a variable name. For example:
```
 &&  yields  &
 ‘’  yields  '  within delimiting single quotes
 ..  yields  .  immediately following a variable name.
```