Xpath function tutorial

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xpath functions: a comprehensive tutorial with examples

xpath (xml path language) is a query language for selecting nodes from an xml or html document. while xpath expressions can be simple, its true power lies in the vast library of functions it provides. these functions allow you to manipulate data, compare values, perform calculations, and much more, enabling you to extract precisely what you need from your xml/html data.

this tutorial will delve deep into xpath functions, covering various categories with detailed explanations, examples, and practical use cases. we'll focus on xpath 1.0, the most widely supported version, but will touch upon xpath 2.0/3.0 differences where relevant.

*understanding function concepts*

before diving into specific functions, let's solidify some fundamental concepts:

*function calls:* functions are invoked using their name followed by parentheses. arguments are passed inside the parentheses, separated by commas. for example: `string-length("hello world")`

*return values:* each function returns a specific data type:
*string:* a sequence of characters (e.g., "hello", "123").
*number:* a floating-point number (e.g., 3.14, 10, -5.2).
*boolean:* `true` or `false`.
*node-set:* a set of xml/html nodes.

*data type conversion:* xpath automatically attempts to convert data types where necessary. for example, it might convert a string to a number if used in an arithmetic operation. however, explicit conversion functions are available (explained later) for better control.

*context node:* many functions operate in the context of a specific node. this "context node" is determined by the preceding xpath expression.

*categorizing xpath functions*

we'll organize the functions into these categories:

1. *string functions:* manipulating and extracting information from strings.
2. *number functions:* performing mathematical calculations.
3. *boolean functions:* evaluating ...

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