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Name

link — A knot/link packet

Synopsis

Content Model 
link ::= (crossings, connections, components,
          tag*,
          (container|textdata|script|attachment|
           tri|link|snappeadata|
           angles|surfaces|hypersurfaces|
           filtercomb|filterprop|filtertrivial|
           anon|anonref)*)
Attributes
NameType
idCDATA
labelCDATA

Added in Regina 7.0

Description

This represents a knot/link packet, one of the many types of packet that together form the packet tree that a user sees when they open a Regina data file.

A knot/link packet stores the diagram of an oriented link in 3-dimensional space.

The number of crossings in the diagram and the signs of these crossings are stored in the child crossings element, and the connections between these crossings are stored in the child connections element. The child components element stores a starting point for each component of the link.

There are several child XML elements that are common to all packet types. The tag elements represent an arbitrary set of string “tags” that users can attach to a packet to help organise their data. The remaining child elements list all of Regina's packet types (container, textdata, etc.), and these represent the immediate children of this packet in the packet tree.

Parents

The following elements can contain any packet element (including this): angles, anon, anonref, attachment, container, filtercomb, filterprop, filtertrivial, hypersurfaces, link, regina, script, snappeadata, surfaces, textdata, tri. This list includes all packet types, as well as the top-level element regina.

Children

The following elements occur in link, and are specific to the knot/link packet type: components, connections, crossings.

The following children can occur in all packet elements: angles, anon, anonref, attachment, container, filtercomb, filterprop, filtertrivial, hypersurfaces, link, script, snappeadata, surfaces, tag, textdata, tri. This list includes all packet types, as well as the tag element for tagging individual packets.

Attributes

The following attributes are common to all packet types:

id

A unique identifier for this packet. Packets are not required to have IDs, but when they are present they must be distinct (i.e., no packets in the same file may share the same ID). IDs do not need to be human-readable, must not contain leading or trailing whitespace, and must not be empty strings. Currently, IDs are built from base 64 hashes of the underlying C++ pointers.

The purpose of these packet IDs is to allow other packets to reference this packet (for instance, so that a script packet can store references to its variables).

IDs are not required to stay the same across subsequent loads and saves of the same file. In other words, if you load a file and save it again, the packet IDs are allowed to change.

label

The name given by the user to this particular packet within the overall packet tree.

Example

The following XML snippet represents the Whitehead link. 

<link label="Whitehead link">
<crossings size="5">
- - + + -
</crossings>
<connections>
_1 ^1
_2 ^4
_4 ^3
_0 ^2
_3 ^0
</connections>
<components size="2">
^0 _0
</components>
</link>
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