About a webcontrol, the best HN can currently do is to retrieve a web page and place it into a text file but it cannot display/render the webpage as RB can do.
Rendering a web page is a huge task and the URLexistsFN simply allows an HN program to retrieve then process a web page and look for specific data within it. Perhaps looking for tags and then extracting the data within those tags. In theory it is possible with the current version of HN to create your own algorithms to display simple web pages in a canvas but it would need a lot of programming.
Perhaps you have seen the HN Web Alarm project it also uses a the URLexistsFN to retrieve a file from the Tigabyte website..
this is the following of what i took out of my source code.
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@This example finds your IP address using the website 'www.whatismyip.org'. If successful
@it puts the IP address number into field 1.
Local webaddr,yield,timeout,filename,okay
@ Set params for URLexists function
HTTPSetHeaderName('User-Agent')
HTTPSetHeaderValue('My Web Browser')
Put 'http://www.msn.com/' into webaddr
Put 1 into yield
Put 30 into timeout
Put 'webtext.txt' into filename
Put URLexistsFN(webaddr,yield,timeout,filename) into okay
Put 'Loading' into field 1
@ If okay then write IP to field 1
If okay=1 Then
put '' into field 1
Local h1,sdata
OpenTReadLoc(filename,h1)
ReadTLine(h1,sdata)
Put sdata After field 1
CloseTRead(h1)
Else
Put 'unsuccessful' into field 1
EndIf