Format multi-line string contents

CHANGELOG.md

@@ -7,6 +7,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
 
+### Added
+
+- Formatting for multiline string interior whitespace. Enabled by default with new setting `format_multiline_strings`.
+  1. Indentation is normalised to align the trailing quote with the leading quote. Lines in the
+    middle are adjusted to retain their original significant leading whitespace.
+  2. Internal line endings are normalised to match the configured line ending.
+  3. Invalid multiline strings are left untouched.
+
 ## [0.6.0] - 2025-08-25
 
 ### Fixed

core/CHANGELOG.md

@@ -7,6 +7,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Added
+
+- Setting to enable internal formatting of multiline strings: `OptimisingLineFormatterSettings.format_multiline_strings`.
+
+### Changed
+
+- In order to support mutation of token contents, a few APIs have been adjusted.
+  - Methods of `FormattedTokens` including `new_from_tokens`, `new`, `get_tokens`, and `get_token`
+    were adjusted to either expect exclusive references to tokens as arguments, or return exclusive
+    references to tokens as part of the result.
+  - `FormattedTokens::get_tokens_mut` was added to return a mutable reference to the underlying
+    vector, providing a way to mutate the tokens.
+  - `Token::set_content` was added.
+
 ## 0.6.0 - 2025-08-25
 
 ### Fixed