Insert

The insert action inserts items into an instance, and has 5 attributes, all optional:

ref or bind that gives a destination sequence (default an empty sequence);
context, that gives the context for the ref (default the element context);
origin, evaluated in the in-scope evaluation context, that specifies a source sequence, (default, the last item in the destination sequence);
at, that specifies a numeric location in the destination sequence for the insertion (default, the size of the destination sequence);
position, whether to insert before or after the destination location (default after).

After successful conclusion, an xforms-insert event is dispatched to the destination instance with appropriate context information, including a list of the items inserted.

An insert action has no effect if:

the source sequence is empty (which includes the destination sequence being empty, with no non-default source sequence);
the destination location, or its parent is read-only;
the at attribute, evaluated as a number in the Element Evaluation Context and rounded to the nearest integer, is not a number or is out of bounds of a non-empty destination sequence.

Each item of the source sequence is inserted:

next to the destination location, if the destination sequence is non-empty,
into the context node otherwise, ignoring at and position.

If an item to be inserted is a node, it and its entire subtree are copied and inserted; if it is an atomic value, a text node is created and inserted.

An item is not inserted:

if it or the destination location is a root node (the parent of a root element);
if it doesn't match the location where it is being inserted (for instance, an attribute may not be a sibling of an element).

If the destination location is a root element, the item must be an element, and it replaces the destination element and its children, otherwise the item is not inserted.

If the destination sequence has sort properties, the inserted nodes will end up sorted accordingly, regardless of the at and position attributes.

	Document	Element	Attribute	Text	NS	PI	Comment
Document	X	Replaces root element	X	X?	X?	Insert?	Insert?
Root element	X	Replaces root element	Becomes/replaces attr	Sibling?	Insert/replace	Insert	Insert
Element	X	Sibling unless parent is doc	Becomes/replaces attr	Sibling	Insert/replace	Insert	Insert
Attribute	X	X	Replaces or sibling	X?	X	X	X
Text	X	Sibling unless parent is doc	X	Concat	X	Sibling	Sibling
NS	X	X	X	X	Sibling or replace	X	X
PI	X	Sibling unless parent is doc	X	Sibling	X	Sibling	Sibling
Comment	X	Sibling unless parent is doc	X	Sibling	X	Sibling	Sibling

Trying to make the <insert/> element more readable

https://www.w3.org/community/xformsusers/wiki/XForms_2.0#The_insert_Element

The text for the insert element is two pages of fairly opaque text, which I have recently thought about a lot trying to make it more digestible.

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The target-sequence is obtained from the element evaluation context.

If the target-sequence is empty:
- if there is no origin attribute, the insert action has no effect
- if there is an origin attribute:
  The origin-sequence is obtained
  - if the origin-sequence is empty, the insert action has no effectthe insert action has no effect
  - if the origin-sequence is non-empty:
    the nodes of the origin-sequence are added one by one to the context element
If the target-sequence is non empty:
- if there is no origin attribute:
  the last element of the target-sequence is copied, and added to the target sequence
- if there is an origin attribute:
  the origin-sequence is obtained
  - if the origin-sequence is empty, the insert action has no effect
  - if the origin-sequence is non empty:
    the nodes are added one by one to the target sequence.

An origin sequence is obtained by evaluating the origin attribute in the in-scope evaluation context, and removing any root nodes (parents of document elements) from the resulting sequence. An implementation may choose not to include namespace nodes in the origin-sequence, in particular if the namespace axis is not supported or if inserting the namespace node would make the data model inconsistent.

An element is added to a sequence:

if the sequence has sort properties:
by inserting the element at the appropriate sort position in the sequence
if the sequence does not have sort properties:
by inserting the element according to the at and position values:
- if the at attribute is present:
  it is evaluated as a number in the Element Evaluation Context and rounded to the nearest integer;
  if the result is not a number, is less than 1 or is greater than the target-sequence size: the insert action has no effect.
- if the at attribute is not present:
  The size of the target-sequence is used
- if the position attribute is present, its value is used, otherwise the value "after".

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The insert action has no effect

if the target sequence is empty, and either there is no origin attribute, or the origin sequence is empty
if the target sequence is not empty and there is an origin attribute, and the origin sequence is empty
if the at attribute does not evaluate to a number, or when used is less than 1 or greater than the size of the target sequence.
if the target sequence or its parent is read-only