---
title: Normalize text for downstream systems
summary: Fold Unicode punctuation to ASCII and filter text by character class.
status: draft
owner: saif-docgen
last_reviewed: 2026-09-15
library: SAIF.Framework.Common
reference_type: package
operation_id: OP-032
trigger: Caller prepares text for a fixed-format file, a legacy system, or display*
---

# Normalize text for downstream systems

Fold Unicode punctuation to ASCII and filter text by character class, triggered when caller prepares text for a fixed-format file, a legacy system, or display*.

| Field | Value |
| --- | --- |
| **Operation ID** | OP-032 |
| **Trigger** | Caller prepares text for a fixed-format file, a legacy system, or display* |
| **Inputs** | `string` |
| **Outputs** | `string` |
| **Primary components** | ``StringExtensions.ReplaceUnicodeCharactersWithAscii`; `StringUtilities.Digits` / `Letters` / `LettersOrDigits` / `Punctuation` / `Symbols` / `ControlCharacters` / `RemoveControlCharacters` / `RemoveWhiteSpaces`` |
| **Entry point** | `Common/SAIF.Common/Extensions/StringExtensions.cs` |

## Steps

1. `ReplaceUnicodeCharactersWithAscii` substitutes `string.Empty` for a null input (via `GenericExtensions.IsNull`) so it never throws. ([BR-074](../business-rules.md#br-074-non-ascii-typographic-characters-are-folded-to-ascii-equivalents-before-text-leaves-the-system))
2. Fold 4 curly/angled single-quote code points to `'`, 6 double-quote code points to `"`, 6 bullet code points to `*`, 8 dash/hyphen code points to `-`, and the NUL character to a space, in one chained `Replace` expression. ([BR-074](../business-rules.md#br-074-non-ascii-typographic-characters-are-folded-to-ascii-equivalents-before-text-leaves-the-system))
3. Each `StringUtilities` filter null-guards the input (returning `""`), then walks the character array retaining only characters matching the corresponding `char.Is*` predicate (`IsDigit`, `IsLetter`, `IsLetterOrDigit`, `IsPunctuation`, `IsSymbol`, `IsControl`). ([BR-075](<../business-rules.md#br-075-character-class-filters-retain-(or%2C-for-the-remove-variants%2C-exclude)-exactly-the-characters-matching-the-corresponding-char.is-predicate%2C-and-treat-a-null-input-as-an-empty-string>))
4. `RemoveControlCharacters` and `RemoveWhiteSpaces` invert the predicate, retaining everything that is not a control character / not whitespace. ([BR-075](<../business-rules.md#br-075-character-class-filters-retain-(or%2C-for-the-remove-variants%2C-exclude)-exactly-the-characters-matching-the-corresponding-char.is-predicate%2C-and-treat-a-null-input-as-an-empty-string>))

## Process flow

The following diagram visualizes this operation's control flow.

```mermaid
flowchart TD
	Start(["Caller normalizes text for<br>a downstream system"]) --> Null{"ReplaceUnicodeCharactersWithAscii:<br>input is null?"}
	Null -->|Yes| Empty(["Return string.Empty"])
	Null -->|No| Fold["Fold quotes, bullets, dashes,<br>and NUL to ASCII equivalents"]
	Fold --> Filter["StringUtilities filter: guard input,<br>retain chars matching char.Is* predicate"]
	Filter --> Invert["Remove variants invert predicate:<br>retain non-matching characters"]
	Invert --> End(["Normalized string returned"])
```

## Related documentation
- [Operations and processes](../operations-processes.md)
- [Business rules](../business-rules.md)

> **Note:** Statements marked with * were inferred from code structure, naming conventions, or contextual evidence where direct confirmation was not available in source artifacts.

## Sources
- `Common/SAIF.Common/Extensions/StringExtensions.cs`
- `Common/SAIF.Common/Utility/StringUtilities.cs`