Robert Wilton <[email protected]> wrote: > > > On 23/10/2017 10:10, Martin Bjorklund wrote: > > Andy Bierman <[email protected]> wrote: > >> On Fri, Oct 20, 2017 at 9:24 AM, Robert Wilton <[email protected]> > >> wrote: > >> > >>> Hi Lada, > >>> > >>> Thanks for the explanation, that makes sense. > >>> > >>> > >>> On 20/10/2017 16:27, Ladislav Lhotka wrote: > >>> > >>>> Hi Rob, > >>>> > >>>> Robert Wilton <[email protected]> writes: > >>>> > >>>> Hi, > >>>>> XPATH 1.0 defines the following three node-type tests: > >>>>> > >>>>> 1) comment() > >>>>> 2) processing-instruction(<opt arg>) > >>>>> 3) text() > >>>>> > >>>> For completeness, node() is the fourth one. > >>>> > >>>> My assumption is that a YANG tree doesn't contain any nodes of type > >>>>> 'comment' or 'processing-instruction' and hence these filters would > >>>>> never match any nodes. > >>>>> > >>>> Yes. FWIW, Yangson library raises NotSupported exception upon > >>>> encountering these. > >>>> > >> But a server or client should ignore PIs, not reject the XML. > >> > >> I think text() and node() are just filter tests. > >> > >> /foo/*[text()] would return all the child nodes of /foo that are leaf > >> or > >> leaf-list > >> > >> text() returns a boolean (0 or 1). Do not use it for value testing: > > No. text() will select the text node children of the context node. > This is presumably because text() is evaluated as "child::text()".
Yes. > >> /foo/*[text() = 'fred'] // wrong! > > This actually works. text() selects all text nodes (just one for a > > leaf), and then that text node is compared to the string 'fred'. > For clarity, am I right in my interpretation that a leaf is not itself > a text node, but instead a leaf is an element node that contains a > direct child text node? Yes. > Presumably, it is only leaf and leaf-list element nodes that can have > these direct child text nodes. Yes. > I can see how this make sense for a XML document, but it does feel a > bit non intuitive for a YANG data tree Maybe, but since we use XPath, we need to conform to the data model used by XPath (see section 5 of the xpath spec). > and it may be helpful if this > is documented somewhat ... RFC 7950 refers to the data model of XPath (See section 6.4 of RFC 7950), but I agree that it could have had more text. Specifically, it could have stated how nodes are mapped to elements, that only leaf/leaf-list have text nodes; that annotations are mapped to attribute nodes (ok, not really in 7950...); that there are no processing-instruction and comment nodes. > > /foo/*[. = 'fred'] // correct > > Presumably this test isn't quite the same, since child container and > list nodes would also be included in the comparison (i.e. by > concatenating all their descendant leaf values together into a single > string) > whereas the expression with the text() check will only > include the values of direct child leaf and leaf-list nodes (as YANG > is currently defined today). Yes. /martin _______________________________________________ netmod mailing list [email protected] https://www.ietf.org/mailman/listinfo/netmod
