Explicit lineBreak are needed

[Ducasse]

Imagine the following text

a b **bold** 
d
e

plainText
	^ ( self children collect: [:each | each plainText ] ) joinUsing: ' '

plainText should be rewritten only text and it is not bijective so we lose completely the structure.

We should represent explictily lineBreak as children

[Ducasse]

This issue is different from double space.