line1
%%[
    SET @test = 'bla bla'
]%%
line2 %%= ContentBlockByName("Content Builder\dont strip non ssjs content") =%% still line2 line3
<script runat="server">
    Platform.Function.ContentBlockByName(
        "Content Builder\\dont strip non ssjs content"
    );
    Platform.Function.ContentBlockByKey("testExisting_htmlblock1");
</script>