Positional parameters

A positional parameter is a parameter that must be entered in a specific position of the input string syntax and before the keyword parameters.

The following are examples of positional parameters:

```
Grammar: ZDSMG ACTION SDA
Input string: ZDSMG ACTION SDA
```
- ZDSMG is a positional parameter and must always be the first parameter.
- ACTION is a positional parameter and must always be the second parameter.
- SDA is positional parameter and must always be the third parameter.
```
Grammar: P1 cc.dd (xx)*
Input string: P1 AB.01 F0.E1.D2
```
- P1 is a positional parameter and must always be the first parameter.
- cc.dd is a positional parameter and must always be the second parameter.
- (xx)* is positional parameter and must always be the third parameter.

A positional parameter can:

Match specific characters

Examples:

```
Grammar: ABC
Input string must be: ABC
```

Grammar: Abc
Input string can be: A or AB or ABC

Match character types: a, c, d, u, w, x, + and *

Examples:

Grammar: acd*
Input string can be: AX1 or 0Y12 or ZZ123 and so on

Grammar: d+++
Input string can be one to four digits: 1 or 21 or 345 or 5555
and so on

Be a list.

Example:

Grammar: acd.xw
Input string can be:
 For the whole list:  0A1.F*
 For the first item:  AB9.
 For the second item:  .0A

Be a wildcard list.

Example:

Grammar: (cd)*
Input string: A1, or F2.C3, or D4.E5.Z2, or any combination of cd
repeated up to 20 times. Each item in the input string must be delimited
from the following item by a period (.).