Location paths¶

A location path is how XPath points at nodes in a document. It is a sequence of steps separated by /. Each step selects a set of nodes relative to the current context; the next step then runs once from each of those nodes, and the results are gathered together. A path is read left to right, narrowing or shifting the context one step at a time.

For these examples the running catalog gains a genre attribute on each cd, and the first CD keeps an optional <year> child while the others omit it:

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<catalog>
  <cd genre="rock"><title>Empire Burlesque</title><artist>Bob Dylan</artist><price>10.90</price><year>1985</year></cd>
  <cd genre="pop"><title>Hide your heart</title><artist>Bonnie Tyler</artist><price>9.90</price></cd>
  <cd genre="country"><title>Greatest Hits</title><artist>Dolly Parton</artist><price>9.90</price></cd>
</catalog>

Absolute and relative paths¶

A leading / anchors the path at the document root — the invisible node that sits above the outermost element. From there catalog selects the root element, and catalog/cd reads as "every cd child of the catalog child of the root".

/catalog/cd/title     <!-- (1)! -->

1. Absolute: start at the root, walk down catalog, then cd, then title.

Without the leading /, the path is relative: it begins at whatever the current context node happens to be. If the context is a cd, then title selects that CD's title and cd/title would look for a cd child of the current cd (here, nothing).

cd/title              <!-- relative to the current node -->

The // descendant shorthand¶

// is shorthand for "descendant-or-self": it matches at any depth, not just the immediate child. //title finds every title anywhere in the document, however deeply nested:

//title

It can also appear in the middle of a path. catalog//price selects every price at any depth beneath catalog:

catalog//price

Self, parent, and attributes¶

Two steps refer to the context itself and its parent:

• . is the current node (self).
• .. is the parent of the current node.

So from a title, .. reaches its cd, and ../price reaches that CD's price. . is mostly used to pass the current node to a function or to root a relative path explicitly, as in .//title.

Attributes are addressed with the @ prefix. They are not children, so they need their own step:

cd/@genre             <!-- (1)! -->

1. The genre attribute of each cd.

The union operator¶

| forms the union of two node-sets — every node selected by either side. title | artist selects both the titles and the artists:

catalog/cd/title | catalog/cd/artist

The two operands need not be related — title | @genre is perfectly legal. The result is a single node-set, with the usual node-set rules below.

A step result is a node-set¶

In XPath 1.0 every location path evaluates to a node-set. Three properties follow from that:

• It is conceptually unordered — a set, not a list.
• It contains no duplicates; a node selected by both sides of a | appears once.
• When you consume it — iterate, take [1], or render it — the processor visits the nodes in document order (the order they appear in the source).

This is why (//title)[1] is well defined: the parentheses build the whole node-set first, then positional [1] picks the document-order first node.

Common path shapes¶

Next¶

Every step so far — cd, .., @genre, // — is an abbreviation of a fuller syntax that names a direction through the tree. Axes unfolds those abbreviations and shows the directions you cannot reach without them.