Volume 6A: Motif Programming Manual

There are some situations where it is impractical to place complete information on the clipboard. Some people's cargo

may be "too heavy" for the clipboard to hold indefinitely. Other people may have perishables that don't last very long.

Still others may have information that varies with the state of the world. For these cases, the person with the special

cargo may choose to leave only some information about their cargo rather than the cargo itself. This information

might include its weight, type, name and/or reference number, for example. Potential recipients may then examine the

clipboard and inquire about the cargo without having to get it or even look at it. Only in the event that someone else

wishes to obtain the cargo is the original owner called upon to provide it.

In the Motif world, this scenario describes clipboard data that is available by name. For example, if a client wishes to

place an entire file on the clipboard, it might choose to register the file by name without providing the actual contents

unless someone requests it. This may save a lot of time and resources, since it's possible that no one will request it.

Referencing data this way is very cheap and is not subject to expiration or obsolescence.

When posting messages by name, the client must provide the clipboard with a callback function that returns the actual

data. This callback function may be called by the Motif toolkit at any time, provided another client requests the data.

If the data is time−dependent or subject ...