[TYPO3-core] Different title tag when using "subtitle" field

[Kamil R]

I want to make this situation to happen.
When I fill "subtitle" field I want to make something like that <title>subtitle field only</title>
If subtitle field isn't fill then use simple title field and append custom text <title>title field - custom text</title>

Of course I can do this and write this custom text in the field but when I have many entries to edit it's wasting my time when I would make this happen upon script.

Right now I have something like this in template settings:

# HEAD Title
page.headerData {
#Title TAG
	10 = TEXT
	10 {
		value = <title>
	}
	12 = TEXT
	12 {
		field = subtitle // title
		#page.if.isEmpty.field = title
		override {
			required = 1
			data = levelfield : -1 , subtitle, slide
		}
	}
	14 = TEXT
	14 {
		value = </title>
	}	
}