fixes #19439: add some docs context to migration for .btn-xs and .page-header
fixes #19439: add some docs context to migration for .btn-xs and .page-header

slavanga/bootstrap,9-chirno/chirno,andresgalante/bootstrap,Lyricalz/bootstrap,johnajacob/bootstrap,Hemphill/bootstrap-docs,yuyokk/bootstrap,tomlutzenberger/bootstrap,hebbet/bootstrap,m5o/bootstrap,bardiharborow/bootstrap,yuyokk/bootstrap,frostbitten/bootstrap,jipexu/bootstrap,gijsbotje/bootstrap,copperdesign/bootstrap,seanwu99/bootstrap,wesamco/bootstrap-rtl,stanwmusic/bootstrap,tibo66/bootstrap,slavanga/bootstrap,hebbet/bootstrap,Scoutski/bootstrap,sealocal/bootstrap,kvlsrg/bootstrap,Hemphill/bootstrap-docs,TheFridayInstitute/bootstrap,joblocal/bootstrap,n054/bootstrap,andresgalante/bootstrap,copperdesign/bootstrap,Scoutski/bootstrap,bardiharborow/bootstrap,vsn4ik/bootstrap,GerHobbelt/bootstrap,Hightrack/bootstrap,9-chirno/chirno,jipexu/bootstrap,gijsbotje/bootstrap,vsn4ik/bootstrap,johnajacob/bootstrap,9-chirno/chirno,Lyricalz/bootstrap,tagliala/bootstrap,supergibbs/bootstrap,GerHobbelt/bootstrap,tibo66/bootstrap,slavanga/bootstrap,lipis/bootstrap,NCARB/bootstrap,seanwu99/bootstrap,coliff/bootstrap,JumpLinkNetwork/bootstrap-backward,SweetProcess/bootstrap,peterblazejewicz/bootstrap,zalog/bootstrap,copperdesign/bootstrap,realcrowd/bootstrap,Scoutski/bootstrap,igoynawamreh/bootstrap,lipis/bootstrap,lemuelbarango/bootstrap,bootstrapbrasil/bootstrap,inway/bootstrap,bootstrapbrasil/bootstrap,fschumann1211/bootstrap,xt0rted/bootstrap,slavanga/bootstrap,GerHobbelt/bootstrap,Delagen/bootstrap,davethegr8/bootstrap,Delagen/bootstrap,creativewebjp/bootstrap,janseliger/bootstrap,wesamco/bootstrap-rtl,tagliala/bootstrap,wesamco/bootstrap-rtl,tomlutzenberger/bootstrap,peterblazejewicz/bootstrap,Scoutski/bootstrap,stanwmusic/bootstrap,tomlutzenberger/bootstrap,jipexu/bootstrap,coliff/bootstrap,frostbitten/bootstrap,yuyokk/bootstrap,janseliger/bootstrap,igoynawamreh/bootstrap,kvlsrg/bootstrap,creativewebjp/bootstrap,joblocal/bootstrap,jipexu/bootstrap,supergibbs/bootstrap,9-chirno/chirno,NCARB/bootstrap,edanbarak/bootstrap,IdanCo/bootstrap,TheFridayInstitute/bootstrap,lipis/bootstrap,lipis/bootstrap,janseliger/bootstrap,TheFridayInstitute/bootstrap,joblocal/bootstrap,n054/bootstrap,nice-fungal/bootstrap,johnajacob/bootstrap,SweetProcess/bootstrap,stanwmusic/bootstrap,afuno/bootstrap,lemuelbarango/bootstrap,vsn4ik/bootstrap,xt0rted/bootstrap,hebbet/bootstrap,edanbarak/bootstrap,seanwu99/bootstrap,vsn4ik/bootstrap,johnajacob/bootstrap,abvalentine/bootstrap,afuno/bootstrap,JumpLinkNetwork/bootstrap-backward,kvlsrg/bootstrap,frostbitten/bootstrap,tjkohli/bootstrap,JumpLinkNetwork/bootstrap-backward,peterblazejewicz/bootstrap,IdanCo/bootstrap,Hemphill/bootstrap-docs,IdanCo/bootstrap,Delagen/bootstrap,twbs/bootstrap,Hightrack/bootstrap,fschumann1211/bootstrap,davethegr8/bootstrap,stanwmusic/bootstrap,yuyokk/bootstrap,SweetProcess/bootstrap,afuno/bootstrap,NCARB/bootstrap,joblocal/bootstrap,n054/bootstrap,TheFridayInstitute/bootstrap,zalog/bootstrap,bootstrapbrasil/bootstrap,n054/bootstrap,bardiharborow/bootstrap,xt0rted/bootstrap,zalog/bootstrap,sealocal/bootstrap,davethegr8/bootstrap,creativewebjp/bootstrap,abvalentine/bootstrap,inway/bootstrap,supergibbs/bootstrap,supergibbs/bootstrap,IdanCo/bootstrap,tibo66/bootstrap,igoynawamreh/bootstrap,nice-fungal/bootstrap,andresgalante/bootstrap,abvalentine/bootstrap,gijsbotje/bootstrap,bardiharborow/bootstrap,tibo66/bootstrap,JumpLinkNetwork/bootstrap-backward,nice-fungal/bootstrap,edanbarak/bootstrap,fschumann1211/bootstrap,SweetProcess/bootstrap,realcrowd/bootstrap,davethegr8/bootstrap,realcrowd/bootstrap,lemuelbarango/bootstrap,Lyricalz/bootstrap,igoynawamreh/bootstrap,Hightrack/bootstrap,sealocal/bootstrap,hebbet/bootstrap,frostbitten/bootstrap,afuno/bootstrap,gijsbotje/bootstrap,andresgalante/bootstrap,twbs/bootstrap,inway/bootstrap,creativewebjp/bootstrap,sealocal/bootstrap,lemuelbarango/bootstrap,seanwu99/bootstrap,NCARB/bootstrap,janseliger/bootstrap,Delagen/bootstrap,edanbarak/bootstrap,Lyricalz/bootstrap,Hemphill/bootstrap-docs,tagliala/bootstrap,copperdesign/bootstrap,xt0rted/bootstrap,realcrowd/bootstrap,abvalentine/bootstrap,tjkohli/bootstrap,m5o/bootstrap,fschumann1211/bootstrap,wesamco/bootstrap-rtl