This warning category is spelled [multiline-strings] by qmllint.

String contains unescaped line terminator, which is deprecated

What happened?

A string spans over multiple lines.

Why is this bad?

Strings spanning multiple lines are a non-standard extension of ECMAScript and deprecated in QML. Use template literals instead.

Example

import QtQuick

Item {
    property string multiLine: "first
second
third"

    property string multiLine2: 'first
second
third'
}

To fix this warning, use template literals or, alternatively, replace the newlines with '\n':

import QtQuick

Item {
    property string multiLine: `first
second
third`
    property string multiLine2: `first
second
third`

    property string alternative: "first\nsecond\nthird"
    property string alternative2: "first\n" +
"second\n" +
"third"
}