Use Lines to manipulate text in an editor control on a line-by-line basis. 

Lines is a TStrings object, so the TStrings methods may be used for Lines to perform manipulations such as counting the lines of text, adding new lines, deleting lines, or replacing lines with new text. But it is not recommended to use standard TStrings methods. 

Instead use TCustomSyntaxMemo methods to manipulate text in the editor, because they support undo and optimized refreshing engine. These methods are: DeleteText, InsertText, MoveText, ReplaceText. 

If you need whole text access for read-only operations (for example, for search or custom analysis), do not use Lines.Text property, instead use direct access to text field Lines.FText. It will be more efficiently, because no string copying will be used.

Although Lines property is implemented as a TStrings descendant, it does not implement the support for associating objects with the strings in the list.

TSyntaxMemo Properties