### Sample Content for HelloWorld Language

Source: https://langium.org/docs/introduction/playground

This section provides sample input content that conforms to the 'HelloWorld' grammar. It demonstrates the usage of the defined 'person' and 'Hello' keywords, including referencing previously defined persons. This content is used to test and validate the grammar's parsing capabilities.

```plaintext
person John
person Jane
Hello John!
Hello Jane!
```

--------------------------------

### Generated Syntax Tree for HelloWorld Content

Source: https://langium.org/docs/introduction/playground

This represents the abstract syntax tree (AST) generated by Langium after parsing the sample 'HelloWorld' content. It shows the hierarchical structure of the parsed data, including types, attributes, and references. This tree is crucial for semantic analysis and code generation.

```json
{
  "$type": "Model", 
  "persons": [
    {
      "$type": "Person", 
      "name": "John"},
    {
      "$type": "Person", 
      "name": "Jane"
}
],
  "greetings": [
    {
      "$type": "Greeting", 
      "person": Reference('#/persons@0')
},
    {
      "$type": "Greeting", 
      "person": Reference('#/persons@1')
}
]
}
```

--------------------------------

### Define HelloWorld Grammar in Langium

Source: https://langium.org/docs/introduction/playground

This code defines the grammar for a simple 'HelloWorld' language using Langium's DSL. It specifies the structure for 'Model', 'Person', and 'Greeting' elements, along with terminal rules for identifiers and whitespace. This grammar serves as the foundation for parsing and analyzing text in the defined language.

```langium
grammar HelloWorld
entry Model:
(persons+=Person | greetings+=Greeting)*;
Person:
'person' name=ID;
Greeting:
'Hello' person=[Person:ID] '!';
hidden terminal WS: /\s+/;
terminal ID: /[_a-zA-Z][\w_]*/;
hidden terminal ML_COMMENT: /\/\*[\s\S]*?\*\//;
hidden terminal SL_COMMENT: /\/\/[^\n\r]*/;
```

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