Hi, @kolkov.
When apply custom class, multiple line are broken to single line.
Actually, it should keep all elements like p, font, ul, li, ol, and font family, etc

For example:

Before apply custom class:
<font face="Arial">aaaa</font><p><font face="Arial">bbbb</font></p><p><font face="Arial">ccccc</font></p>

After apply custom class
<span class="redText">aaaa&#10;bbbb&#10;&#10;ccccc</span>