Incomputing, theInter-Client Communication Conventions Manual (ICCCM orI39L short for "I", 39 letters and "L")[1] is a standard protocol for theX Window System. It specifies conventions forclients of a commonX server aboutselections and cut buffers, communication with thewindow manager andsession manager, manipulation of shared resources, and color characterization.
It was designed byDavid S. H. Rosenthal of theMIT X Consortium from 1987 to 1989.A draft version appeared in March 1988 inX11R2.This was removed fromX11R3.Version 1.0 was released in July 1989 as part ofX11R4.Three window managers in the X11R4 contrib directory implemented support for ICCCM:gwm,olwm andtekwm. Version 1.1 contains an update forcolor characterization andappeared inX11R5.Version 2.0 has many changes in the areas of window management,selections,session management, and resource sharing.It was released in May 1994 as part ofX11R6.
X deliberately specifies "mechanism, not policy" for how windows interact. As such, an additional specification beyond the X protocol itself was needed for client interoperation.
The ICCCM specifies cut and paste buffers, window manager interaction, session management, how to manipulate shared resources and how to manage device colours. These low-level functions are generally implemented withinwidget toolkits ordesktop environments. This isolates application programmers from working directly with the ICCCM itself, as this functionality is delegated to the implementing toolkit.
The ICCCM has received some criticism for being ambiguous and difficult to implement correctly.[1][2]This was acknowledged in the preface of version 2.0, stating that it aimed"to fix problems with earlier drafts, and to improve readability and understandability".
Furthermore, some parts may be obsolete or no longer practical to implement.[3]TheExtended Window Manager Hints (EWMH) is a more recent standard, which, according to itsintroduction: "builds on the ICCCM, which defines window manager interactions at a lower level.The ICCCM does not provide ways to implement many features that modern desktop users expect."But it also states: "Clients which aim to fulfill this specification MUST adhere to theICCCM on which this specification builds." insofar the EWMH doesn't overrule.
Freedesktop.org notes that"historically, X clients have not handled cut-and-paste in a consistent way"and formulates additional guidelines in aclipboards-specArchived 2021-02-17 at theWayback Machine.
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