The AddAttribute(xmlTree, attr) command creates a new XML element from a given one by adding the specified attributes. The AddAttribute(xmlTree, attrName, attrValue) form of the calling sequence is equivalent to the AddAttribute(xmlTree, attr) form.

The input tree xmlTree must not already have an attribute with the specified attribute name $\mathrm{attrName}$. The behavior of this function is unspecified if the XML tree xmlTree already has an attribute named attrName.

The attribute encoded as attrName = attrValue is added to the attributes of xmlTree, and the new XML tree is returned. The position of the new attribute among any other attributes that may already exist in the tree is unspecified.

$\mathrm{with}\left(\mathrm{XMLTools}\right)\:$

$\mathrm{AddAttribute}\left(\mathrm{XMLElement}\left(''a''\,\left[''foo''=''2''\right]\,\mathrm{XMLElement}\left(''b''\,\left[\right]\,''some\; text''\right)\right)\,''colour''\,''red''\right)$

$\mathrm{\_XML\_Element}\left(\mathrm{\_XML\_ElementType}\left(''a''\right)\,\left[\mathrm{\_XML\_Attribute}\left(\mathrm{\_XML\_AttrName}\left(''foo''\right)\,\mathrm{\_XML\_AttrValue}\left(''2''\right)\right)\,\mathrm{\_XML\_Attribute}\left(\mathrm{\_XML\_AttrName}\left(''colour''\right)\,\mathrm{\_XML\_AttrValue}\left(''red''\right)\right)\right]\,\left[\mathrm{\_XML\_Element}\left(\mathrm{\_XML\_ElementType}\left(''b''\right)\,\left[\right]\,\left[\mathrm{\_XML\_Text}\left(''some\; text''\right)\right]\right)\right]\right)$

$\mathrm{AddAttribute}\left(\mathrm{XMLElement}\left(''a''\,\left[''foo''=''2''\right]\,\mathrm{XMLElement}\left(''b''\,\left[\right]\,''some\; text''\right)\right)\,''colour''=''blue''\right)$

$\mathrm{\_XML\_Element}\left(\mathrm{\_XML\_ElementType}\left(''a''\right)\,\left[\mathrm{\_XML\_Attribute}\left(\mathrm{\_XML\_AttrName}\left(''foo''\right)\,\mathrm{\_XML\_AttrValue}\left(''2''\right)\right)\,\mathrm{\_XML\_Attribute}\left(\mathrm{\_XML\_AttrName}\left(''colour''\right)\,\mathrm{\_XML\_AttrValue}\left(''blue''\right)\right)\right]\,\left[\mathrm{\_XML\_Element}\left(\mathrm{\_XML\_ElementType}\left(''b''\right)\,\left[\right]\,\left[\mathrm{\_XML\_Text}\left(''some\; text''\right)\right]\right)\right]\right)$

$\mathrm{AddAttribute}\left(\mathrm{XMLElement}\left(''a''\,\left[''foo''=''2''\right]\,\mathrm{XMLElement}\left(''b''\,\left[\right]\,''some\; text''\right)\right)\,''size''=2\right)$

Error, (in XMLTools:-AddAttribute) invalid input: XMLTools:-NSXML:-addAttribute2 expects its 2nd argument, attr, to be of type string = string, but received "size" = 2