Module select 

Selection: hit-testing, the selection range, and text extraction.

Selection is a document position pair, not a pixel pair. A Caret names (message, source-within-message, byte offset), so the selection survives everything that moves pixels around — a resize re-wraps, a zoom rescales, an image finishes decoding and grows its row, a history batch prepends above. xtext stored mark_start / mark_end as byte offsets on each textentry plus select_start_x/y in widget coordinates, which is why its selection behaves oddly across a resize mid-drag.

The engine deliberately owns none of the interaction — no notion of button state, drag, or double-click. It answers three questions and the widget does the rest:

• where in the document is this pixel? ([ChatBuffer::hit_test])
• what does the region between two carets look like? (Selection)
• what text does that region contain? ([ChatBuffer::selected_text])

Structs

Caret

A document position.

Selection

An ordered selection range.

Enums

RowSelection

How far a selection extends within one row.

Functions

source_rank

Visual order of a row’s texts.