Annotations

Annotations are metadata declarations that provide additional information about types, interfaces, and properties.

Purpose

Annotations serve multiple purposes:

• UI metadata - Labels, placeholders, descriptions for form generation
• Validation constraints - Min/max values, patterns, length restrictions
• Database metadata - Collection names, indexes, field strategies
• Documentation - Descriptions and multi-line documentation
• Custom metadata - Any domain-specific information

Where to Apply

Annotations can be applied anywhere:

@meta.description 'User entity'    // Interface annotation
export interface User {
    @meta.id                       // Property annotation
    id: string
}

@expect.minLength 3                // Type annotation
export type Username = string

Annotation Inheritance

Type to Property

When a property uses a type with annotations, annotations merge with property having priority:

@expect.minLength 3
@expect.maxLength 20
export type Username = string

export interface User {
    @expect.maxLength 15    // Overrides type's maxLength
    username: Username       // Inherits minLength: 3, gets maxLength: 15
}

Property References

When a property references another property, annotations merge in order:

1. Final type annotations
2. Referenced property annotations
3. Current property annotations (highest priority)

Merge Strategies

When annotations are merged (from type inheritance, property references, or ad-hoc annotations), the merge strategy determines how same-named annotations combine:

Replace (default) — Higher-priority annotations replace lower-priority ones entirely:

@expect.min 3
export type PositiveInt = number

export interface Config {
    @expect.min 10          // Replaces type's @expect.min 3
    threshold: PositiveInt   // Result: @expect.min is 10
}

Append — Both values are kept, accumulating into an array:

@expect.pattern '^[a-z]+$', '', 'Must be lowercase'
export type SafeString = string

export interface Form {
    @expect.pattern '^\S+$', '', 'No spaces'
    code: SafeString
    // Result: both patterns are validated
}

The strategy is configured per annotation via AnnotationSpec. Most annotations use replace. The built-in @expect.pattern uses append.

Repeatable Annotations

Annotations marked with multiple: true can appear more than once on the same node. Their values are stored as arrays:

export interface User {
    @expect.pattern '^[A-Z]', '', 'Must start with uppercase'
    @expect.pattern '.{3,}', '', 'Must be at least 3 characters'
    name: string
}

When merged, how repeated annotations combine depends on the merge strategy:

• multiple: true + replace (default) — The higher-priority set replaces the entire array
• multiple: true + append — Values from both sides are concatenated into a single array

Annotation Syntax

@meta.label 'User Name'           // With argument
@meta.sensitive                   // Flag (no argument)
@expect.pattern "^[A-Z]", "i"     // Multiple arguments
@meta.documentation 'Line 1'      // Can be repeated
@meta.documentation 'Line 2'

Arguments can be optional. Annotations without arguments are flag annotations.

Core Annotations

Atscript provides common-purpose annotations:

Meta Annotations (@meta.*)

• @meta.label 'text' - Human-readable label
• @meta.id or @meta.id 'name' - Marks identifier field
• @meta.description 'text' - Field description
• @meta.documentation 'text' - Multi-line docs (repeatable)
• @meta.placeholder 'text' - UI placeholder text
• @meta.sensitive - Marks sensitive data
• @meta.readonly - Read-only field
• @meta.isKey - Key field in arrays for lookups

Validation Annotations (@expect.*)

• @expect.minLength 5 - Minimum string/array length
• @expect.maxLength 100 - Maximum string/array length
• @expect.min 0 - Minimum number value
• @expect.max 100 - Maximum number value
• @expect.int - Must be integer
• @expect.pattern "regex", "flags", "message" - Pattern validation (repeatable)

Next Steps

• Ad-hoc Annotations — annotate existing types without modifying their definition
• Custom Annotations — define your own annotation types
• Metadata — access annotations at runtime