# Find nodes that match a group of CSS selectors in an XML tree. The purpose of these functions is to mimic the functionality of the `querySelector` and `querySelectorAll` functions present in Internet browsers. This is so we can succinctly query an XML tree for nodes matching a CSS selector. Namespaced functions `querySelectorNS` and `querySelectorAllNS` are also provided to search relative to a given namespace. ```r querySelector(doc, selector, ns = NULL, ...) querySelectorAll(doc, selector, ns = NULL, ...) querySelectorNS(doc, selector, ns, prefix = "descendant-or-self::", ...) querySelectorAllNS(doc, selector, ns, prefix = "descendant-or-self::", ...) ``` ## Arguments - `doc`: The XML document or node to be evaluated against. - `selector`: A selector used to query `doc`. This must be a single character string. - `ns`: The namespace that the query will be filtered to. This is a named list or vector which has as its name a namespace, and its value is the namespace URI. This can be ignored for the un-namespaced functions. - `prefix`: The prefix to apply to the resulting XPath expression. The default or `""` are most commonly used. - `...`: Parameters to be passed onto `css_to_xpath`. ## Details The `querySelectorNS` and `querySelectorAllNS` functions are convenience functions for working with namespaced documents. They filter out all content that does not belong within the given namespaces. Note that when searching for particular elements in a selector, they must have a namespace prefix, e.g. `"svg|g"`. The namespace argument, `ns`, is simply passed on to `getNodeSet` or `xml_find_all` if it is necessary to use a namespace present within the document. This can be ignored for content lacking a namespace, which is usually the case when using `querySelector` or `querySelectorAll`. ## Returns For `querySelector`, the result is a single node that represents the first matched node from a selector. If no matching nodes are found, `NULL` is returned. For `querySelectorAll`, the result is a list of XML nodes. This list may be empty in the case that no match is found. The `querySelectorNS` and `querySelectorAllNS` functions return the same type of content as their un-namespaced counterparts. ## References CSS3 Selectors [https://www.w3.org/TR/css3-selectors/](https://www.w3.org/TR/css3-selectors/), XPath [https://www.w3.org/TR/xpath/](https://www.w3.org/TR/xpath/), querySelectorAll [https://developer.mozilla.org/en-US/docs/DOM/Document.querySelectorAll](https://developer.mozilla.org/en-US/docs/DOM/Document.querySelectorAll) and [http://www.w3.org/TR/selectors-api/#interface-definitions](http://www.w3.org/TR/selectors-api/#interface-definitions). ## Author(s) Simon Potter ## Examples ```r hasXML <- require(XML) hasxml2 <- require(xml2) if (!hasXML && !hasxml2) return() # can't demo without XML or xml2 packages present parseFn <- if (hasXML) xmlParse else read_xml # Demo for working with the XML package (if present, otherwise xml2) exdoc <- parseFn('') querySelector(exdoc, "#anid") # Returns the matching node querySelector(exdoc, ".aclass") # Returns the matching node querySelector(exdoc, "b, c") # First match from grouped selection querySelectorAll(exdoc, "b, c") # Grouped selection querySelectorAll(exdoc, "b") # A list of length one querySelector(exdoc, "d") # No match querySelectorAll(exdoc, "d") # No match # Read in a document where two namespaces are being set: # SVG and MathML svgdoc <- parseFn(system.file("demos/svg-mathml.svg", package = "selectr")) # Search for

querySelectorAll function