org.eclipse.xtext.ui.editor.formatting2.ContentFormatter.initRequest(IXtextDocument, IRegion, XtextResource, FormatterRequest)

this one calls the method. it uses FormatterPreferenceValuesProvider which is usually bound in abstractyourdsluimodule

public void configureFormatterPreferences(Binder binder) {
binder.bind(IPreferenceValuesProvider.class).annotatedWith(FormatterPreferences.class).to(FormatterPreferenceValuesProvider.class);
}

FormatterPreferenceValuesProvider delegates to IWhitespaceInformationProvider which is bound in eclipse to
PreferenceStoreWhitespaceInformationProvider by default.

which again delegates to PreferenceStoreIndentationInformation

which reads spaces for tabs.

Model returns Model: {Model}
    'Model' name=EString
    '{'
        ('Version' version=EString)?
        ('Description' description=EString)?
        elements+=ModelElement*
    '}';

package epc.text.formatting2

import epc.Model
import epc.ModelElement
import org.eclipse.xtext.formatting2.AbstractFormatter2
import org.eclipse.xtext.formatting2.IFormattableDocument

class EpcFormatter extends AbstractFormatter2 {

    def dispatch void format(Model stmt, extension IFormattableDocument document) {
        interior(
            stmt.regionFor.keyword('{').prepend[oneSpace].append[newLine],
            stmt.regionFor.keyword('}').prepend[newLine].append[newLine]
        )[indent]

        for (element : stmt.elements) {
            element.format(document)
        }
    }

    def dispatch void format(ModelElement stmt, extension IFormattableDocument document) {
        stmt.prepend[indent].append[newLine]
    }
}