c# - What's the issue with this WPF binding -

what's issue wpf binding

<textbox name="tagnumbertextbox" style="{staticresource textboxstyle}"  width="200" charactercasing="upper" text="{binding tags, path=[0]}"/>

i getting error on text="{binding tags, path=[0]}"

the property 'path' set more once.

however expecting issue because of wcf service binding. wcf service not being invoked.

wpf screen has datacontext has 1 of property tags observable collection. trying bind first element of collection.

when create binding of form {binding foo}, foo component property path. shorthand form can omit path= component.

therefore {binding tags, path=[0]} setting path both tags , [0].

i suspect wanting {binding path=tags[0]} - or in shorthand form {binding tags[0]}

And