Highlight / parse PSI elements inside another PSI element - parsing

Question

I developed a Custom Language plugin based on this this tutorial.
My plugin parses key/value language files with format like below. Values can contain some HTML tags like <br>, <i>, <b>, <span> and \n. So I want to highlight these tags as separate PSI elements inside green PSI elements (values) (see pic). How can I overwrite my rules to get this?
#Section header
KEY1 = First<br>Value
KEY2 = Second\nValue
Bnf rules I use
lngFile ::= item_*
private item_ ::= (property|header|COMMENT|CRLF)
property ::= (KEY? SEPARATOR VALUE?) | KEY {
mixin="someClass"
implements="someClass"
methods=[getKey getValue getName setName getNameIdentifier getPresentation]
}
header ::= HEADER {
mixin="someClass"
implements="someClass"
methods=[getName setName getNameIdentifier getPresentation]
}
Flex
%%
%class LngLexer
%implements FlexLexer
%unicode
%function advance
%type IElementType
%eof{ return;
%eof}
CRLF=\R
WHITE_SPACE=[\ \n\t\f]
FIRST_VALUE_CHARACTER=[^ \n\f\\] | "\\"{CRLF} | "\\".
VALUE_CHARACTER=[^\n\f\\] | "\\"{CRLF} | "\\".
END_OF_LINE_COMMENT=("//")[^\r\n]*
HEADER=("#")[^\r\n]*
SEPARATOR=[:=]
KEY_CHARACTER=[^:=\ \n\t\f\\] | "\\ "
%state WAITING_VALUE
%%
<YYINITIAL> {END_OF_LINE_COMMENT} { yybegin(YYINITIAL); return LngTypes.COMMENT; }
<YYINITIAL> {HEADER} { yybegin(YYINITIAL); return LngTypes.HEADER; }
<YYINITIAL> {KEY_CHARACTER}+ { yybegin(YYINITIAL); return LngTypes.KEY; }
<YYINITIAL> {SEPARATOR} { yybegin(WAITING_VALUE); return LngTypes.SEPARATOR; }
<WAITING_VALUE> {CRLF}({CRLF}|{WHITE_SPACE})+ { yybegin(YYINITIAL); return TokenType.WHITE_SPACE; }
<WAITING_VALUE> {WHITE_SPACE}+ { yybegin(WAITING_VALUE); return TokenType.WHITE_SPACE; }
<WAITING_VALUE> {FIRST_VALUE_CHARACTER}{VALUE_CHARACTER}* { yybegin(YYINITIAL); return LngTypes.VALUE; }
({CRLF}|{WHITE_SPACE})+ { yybegin(YYINITIAL); return TokenType.WHITE_SPACE; }
[^] { return TokenType.BAD_CHARACTER; }