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To extract a group of nodes from an XML document using XPATH, you can use the XPATH expression that matches the nodes you want to extract. The XPATH expression can be used in different contexts such as XML parsers, XSLT transformations, or programming languages. Here are the general steps to extract a group of nodes using XPATH:

Identify the nodes you want to extract - For example, you may want to extract all the <book> elements from an XML document.
Write an XPATH expression that matches the nodes - The XPATH expression should be specific enough to match the nodes you want to extract and general enough to avoid matching unwanted nodes. For example, the XPATH expression for extracting all <book> elements could be "//book".
Apply the XPATH expression to the XML document - Depending on the context, you may use different tools or techniques to apply the XPATH expression to the XML document. For example, if you are using an XML parser, you may call the "getElementsByTagName" method to retrieve the matching nodes. If you are using XSLT, you may use the "select" attribute to specify the XPATH expression. If you are using a programming language like Python, you may use a library like lxml to parse the XML document and evaluate the XPATH expression.

Here is an example of applying an XPATH expression to extract a group of nodes from an XML document using Python and lxml library:

from lxml import etree

# Parse the XML document
doc = etree.parse("books.xml")

# Define the XPATH expression
xpath_expr = "//book"

# Evaluate the XPATH expression and retrieve the matching nodes
nodes = doc.xpath(xpath_expr)

# Print the nodes
for node in nodes:
    print(etree.tostring(node))