<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="generator" content="Asciidoctor 2.0.16">
<title>restrictions(3)</title>
<style>
/*! normalize.css v2.1.2 | MIT License | git.io/normalize */
/* ========================================================================== HTML5 display definitions ========================================================================== */
/** Correct `block` display not defined in IE 8/9. */
article, aside, details, figcaption, figure, footer, header, hgroup, main, nav, section, summary { display: block; }

/** Correct `inline-block` display not defined in IE 8/9. */
audio, canvas, video { display: inline-block; }

/** Prevent modern browsers from displaying `audio` without controls. Remove excess height in iOS 5 devices. */
audio:not([controls]) { display: none; height: 0; }

/** Address `[hidden]` styling not present in IE 8/9. Hide the `template` element in IE, Safari, and Firefox < 22. */
[hidden], template { display: none; }

script { display: none !important; }

/* ========================================================================== Base ========================================================================== */
/** 1. Set default font family to sans-serif. 2. Prevent iOS text size adjust after orientation change, without disabling user zoom. */
html { font-family: sans-serif; /* 1 */ -ms-text-size-adjust: 100%; /* 2 */ -webkit-text-size-adjust: 100%; /* 2 */ }

/** Remove default margin. */
body { margin: 0; }

/* ========================================================================== Links ========================================================================== */
/** Remove the gray background color from active links in IE 10. */
a { background: transparent; }

/** Address `outline` inconsistency between Chrome and other browsers. */
a:focus { outline: thin dotted; }

/** Improve readability when focused and also mouse hovered in all browsers. */
a:active, a:hover { outline: 0; }

/* ========================================================================== Typography ========================================================================== */
/** Address variable `h1` font-size and margin within `section` and `article` contexts in Firefox 4+, Safari 5, and Chrome. */
h1 { font-size: 2em; margin: 0.67em 0; }

/** Address styling not present in IE 8/9, Safari 5, and Chrome. */
abbr[title] { border-bottom: 1px dotted; }

/** Address style set to `bolder` in Firefox 4+, Safari 5, and Chrome. */
b, strong { font-weight: bold; }

/** Address styling not present in Safari 5 and Chrome. */
dfn { font-style: italic; }

/** Address differences between Firefox and other browsers. */
hr { -moz-box-sizing: content-box; box-sizing: content-box; height: 0; }

/** Address styling not present in IE 8/9. */
mark { background: #ff0; color: #000; }

/** Correct font family set oddly in Safari 5 and Chrome. */
code, kbd, pre, samp { font-family: monospace, serif; font-size: 1em; }

/** Improve readability of pre-formatted text in all browsers. */
pre { white-space: pre-wrap; }

/** Set consistent quote types. */
q { quotes: "\201C" "\201D" "\2018" "\2019"; }

/** Address inconsistent and variable font size in all browsers. */
small { font-size: 80%; }

/** Prevent `sub` and `sup` affecting `line-height` in all browsers. */
sub, sup { font-size: 75%; line-height: 0; position: relative; vertical-align: baseline; }

sup { top: -0.5em; }

sub { bottom: -0.25em; }

/* ========================================================================== Embedded content ========================================================================== */
/** Remove border when inside `a` element in IE 8/9. */
img { border: 0; }

/** Correct overflow displayed oddly in IE 9. */
svg:not(:root) { overflow: hidden; }

/* ========================================================================== Figures ========================================================================== */
/** Address margin not present in IE 8/9 and Safari 5. */
figure { margin: 0; }

/* ========================================================================== Forms ========================================================================== */
/** Define consistent border, margin, and padding. */
fieldset { border: 1px solid #c0c0c0; margin: 0 2px; padding: 0.35em 0.625em 0.75em; }

/** 1. Correct `color` not being inherited in IE 8/9. 2. Remove padding so people aren't caught out if they zero out fieldsets. */
legend { border: 0; /* 1 */ padding: 0; /* 2 */ }

/** 1. Correct font family not being inherited in all browsers. 2. Correct font size not being inherited in all browsers. 3. Address margins set differently in Firefox 4+, Safari 5, and Chrome. */
button, input, select, textarea { font-family: inherit; /* 1 */ font-size: 100%; /* 2 */ margin: 0; /* 3 */ }

/** Address Firefox 4+ setting `line-height` on `input` using `!important` in the UA stylesheet. */
button, input { line-height: normal; }

/** Address inconsistent `text-transform` inheritance for `button` and `select`. All other form control elements do not inherit `text-transform` values. Correct `button` style inheritance in Chrome, Safari 5+, and IE 8+. Correct `select` style inheritance in Firefox 4+ and Opera. */
button, select { text-transform: none; }

/** 1. Avoid the WebKit bug in Android 4.0.* where (2) destroys native `audio` and `video` controls. 2. Correct inability to style clickable `input` types in iOS. 3. Improve usability and consistency of cursor style between image-type `input` and others. */
button, html input[type="button"], input[type="reset"], input[type="submit"] { -webkit-appearance: button; /* 2 */ cursor: pointer; /* 3 */ }

/** Re-set default cursor for disabled elements. */
button[disabled], html input[disabled] { cursor: default; }

/** 1. Address box sizing set to `content-box` in IE 8/9. 2. Remove excess padding in IE 8/9. */
input[type="checkbox"], input[type="radio"] { box-sizing: border-box; /* 1 */ padding: 0; /* 2 */ }

/** 1. Address `appearance` set to `searchfield` in Safari 5 and Chrome. 2. Address `box-sizing` set to `border-box` in Safari 5 and Chrome (include `-moz` to future-proof). */
input[type="search"] { -webkit-appearance: textfield; /* 1 */ -moz-box-sizing: content-box; -webkit-box-sizing: content-box; /* 2 */ box-sizing: content-box; }

/** Remove inner padding and search cancel button in Safari 5 and Chrome on OS X. */
input[type="search"]::-webkit-search-cancel-button, input[type="search"]::-webkit-search-decoration { -webkit-appearance: none; }

/** Remove inner padding and border in Firefox 4+. */
button::-moz-focus-inner, input::-moz-focus-inner { border: 0; padding: 0; }

/** 1. Remove default vertical scrollbar in IE 8/9. 2. Improve readability and alignment in all browsers. */
textarea { overflow: auto; /* 1 */ vertical-align: top; /* 2 */ }

/* ========================================================================== Tables ========================================================================== */
/** Remove most spacing between table cells. */
table { border-collapse: collapse; border-spacing: 0; }

meta.foundation-mq-small { font-family: "only screen and (min-width: 768px)"; width: 768px; }

meta.foundation-mq-medium { font-family: "only screen and (min-width:1280px)"; width: 1280px; }

meta.foundation-mq-large { font-family: "only screen and (min-width:1440px)"; width: 1440px; }

*, *:before, *:after { -moz-box-sizing: border-box; -webkit-box-sizing: border-box; box-sizing: border-box; }

html, body { font-size: 100%; }

body { background: #fff; color: #222; padding: 0; margin: 0; font-family: "Helvetica Neue", "Helvetica", Helvetica, Arial, sans-serif; font-weight: normal; font-style: normal; line-height: 1; position: relative; cursor: auto; }

a:hover { cursor: pointer; }

img, object, embed { max-width: 100%; height: auto; }

object, embed { height: 100%; }

img { -ms-interpolation-mode: bicubic; }

#map_canvas img, #map_canvas embed, #map_canvas object, .map_canvas img, .map_canvas embed, .map_canvas object { max-width: none !important; }

.left { float: left !important; }

.right { float: right !important; }

.text-left { text-align: left !important; }

.text-right { text-align: right !important; }

.text-center { text-align: center !important; }

.text-justify { text-align: justify !important; }

.hide { display: none; }

.antialiased { -webkit-font-smoothing: antialiased; }

img { display: inline-block; vertical-align: middle; }

textarea { height: auto; min-height: 50px; }

select { width: 100%; }

object, svg { display: inline-block; vertical-align: middle; }

.center { margin-left: auto; margin-right: auto; }

.spread { width: 100%; }

p.lead, .paragraph.lead > p, #preamble > .sectionbody > .paragraph:first-of-type p { font-size: 1.21875em; line-height: 1.6; }

.subheader, .admonitionblock td.content > .title, .audioblock > .title, .exampleblock > .title, .imageblock > .title, .listingblock > .title, .literalblock > .title, .stemblock > .title, .openblock > .title, .paragraph > .title, .quoteblock > .title, table.tableblock > .title, .verseblock > .title, .videoblock > .title, .dlist > .title, .olist > .title, .ulist > .title, .qlist > .title, .hdlist > .title { line-height: 1.4; color: black; font-weight: 300; margin-top: 0.2em; margin-bottom: 0.5em; }

/* Typography resets */
div, dl, dt, dd, ul, ol, li, h1, h2, h3, #toctitle, .sidebarblock > .content > .title, h4, h5, h6, pre, form, p, blockquote, th, td { margin: 0; padding: 0; direction: ltr; }

/* Default Link Styles */
a { color: #0068b0; text-decoration: none; line-height: inherit; }
a:hover, a:focus { color: #333; }
a img { border: none; }

/* Default paragraph styles */
p { font-family: Noto, sans-serif; font-weight: normal; font-size: 1em; line-height: 1.6; margin-bottom: 0.75em; text-rendering: optimizeLegibility; }
p aside { font-size: 0.875em; line-height: 1.35; font-style: italic; }

/* Default header styles */
h1, h2, h3, #toctitle, .sidebarblock > .content > .title, h4, h5, h6 { font-family: Noto, sans-serif; font-weight: normal; font-style: normal; color: black; text-rendering: optimizeLegibility; margin-top: 0.5em; margin-bottom: 0.5em; line-height: 1.2125em; }
h1 small, h2 small, h3 small, #toctitle small, .sidebarblock > .content > .title small, h4 small, h5 small, h6 small { font-size: 60%; color: #4d4d4d; line-height: 0; }

h1 { font-size: 2.125em; }

h2 { font-size: 1.6875em; }

h3, #toctitle, .sidebarblock > .content > .title { font-size: 1.375em; }

h4 { font-size: 1.125em; }

h5 { font-size: 1.125em; }

h6 { font-size: 1em; }

hr { border: solid #ddd; border-width: 1px 0 0; clear: both; margin: 1.25em 0 1.1875em; height: 0; }

/* Helpful Typography Defaults */
em, i { font-style: italic; line-height: inherit; }

strong, b { font-weight: bold; line-height: inherit; }

small { font-size: 60%; line-height: inherit; }

code { font-family: Consolas, "Liberation Mono", Courier, monospace; font-weight: normal; color: #264357; }

/* Lists */
ul, ol, dl { font-size: 1em; line-height: 1.6; margin-bottom: 0.75em; list-style-position: outside; font-family: Noto, sans-serif; }

ul, ol { margin-left: 1.5em; }
ul.no-bullet, ol.no-bullet { margin-left: 1.5em; }

/* Unordered Lists */
ul li ul, ul li ol { margin-left: 1.25em; margin-bottom: 0; font-size: 1em; /* Override nested font-size change */ }
ul.square li ul, ul.circle li ul, ul.disc li ul { list-style: inherit; }
ul.square { list-style-type: square; }
ul.circle { list-style-type: circle; }
ul.disc { list-style-type: disc; }
ul.no-bullet { list-style: none; }

/* Ordered Lists */
ol li ul, ol li ol { margin-left: 1.25em; margin-bottom: 0; }

/* Definition Lists */
dl dt { margin-bottom: 0.3em; font-weight: bold; }
dl dd { margin-bottom: 0.75em; }

/* Abbreviations */
abbr, acronym { text-transform: uppercase; font-size: 90%; color: black; border-bottom: 1px dotted #ddd; cursor: help; }

abbr { text-transform: none; }

/* Blockquotes */
blockquote { margin: 0 0 0.75em; padding: 0.5625em 1.25em 0 1.1875em; border-left: 1px solid #ddd; }
blockquote cite { display: block; font-size: 0.8125em; color: #365E7A; }
blockquote cite:before { content: "\2014 \0020"; }
blockquote cite a, blockquote cite a:visited { color: #365E7A; }

blockquote, blockquote p { line-height: 1.6; color: #333; }

/* Microformats */
.vcard { display: inline-block; margin: 0 0 1.25em 0; border: 1px solid #ddd; padding: 0.625em 0.75em; }
.vcard li { margin: 0; display: block; }
.vcard .fn { font-weight: bold; font-size: 0.9375em; }

.vevent .summary { font-weight: bold; }
.vevent abbr { cursor: auto; text-decoration: none; font-weight: bold; border: none; padding: 0 0.0625em; }

@media only screen and (min-width: 768px) { h1, h2, h3, #toctitle, .sidebarblock > .content > .title, h4, h5, h6 { line-height: 1.4; }
  h1 { font-size: 2.75em; }
  h2 { font-size: 2.3125em; }
  h3, #toctitle, .sidebarblock > .content > .title { font-size: 1.6875em; }
  h4 { font-size: 1.4375em; } }
/* Tables */
table { background: #fff; margin-bottom: 1.25em; border: solid 1px #d8d8ce; }
table thead, table tfoot { background: #eee; font-weight: bold; }
table thead tr th, table thead tr td, table tfoot tr th, table tfoot tr td { padding: 0.5em 0.625em 0.625em; font-size: inherit; color: #222; text-align: left; }
table tr th, table tr td { padding: 0.5625em 0.625em; font-size: inherit; color: #6d6e71; }
table tr.even, table tr.alt, table tr:nth-of-type(even) { background: #f8f8f8; }
table thead tr th, table tfoot tr th, table tbody tr td, table tr td, table tfoot tr td { display: table-cell; line-height: 1.4; }

body { -moz-osx-font-smoothing: grayscale; -webkit-font-smoothing: antialiased; tab-size: 4; }

h1, h2, h3, #toctitle, .sidebarblock > .content > .title, h4, h5, h6 { line-height: 1.4; }

a:hover, a:focus { text-decoration: underline; }

.clearfix:before, .clearfix:after, .float-group:before, .float-group:after { content: " "; display: table; }
.clearfix:after, .float-group:after { clear: both; }

*:not(pre) > code { font-size: inherit; font-style: normal !important; letter-spacing: 0; padding: 0; background-color: transparent; -webkit-border-radius: 0; border-radius: 0; line-height: inherit; word-wrap: break-word; }
*:not(pre) > code.nobreak { word-wrap: normal; }
*:not(pre) > code.nowrap { white-space: nowrap; }

pre, pre > code { line-height: 1.6; color: #264357; font-family: Consolas, "Liberation Mono", Courier, monospace; font-weight: normal; }

em em { font-style: normal; }

strong strong { font-weight: normal; }

.keyseq { color: #333333; }

kbd { font-family: Consolas, "Liberation Mono", Courier, monospace; display: inline-block; color: black; font-size: 0.65em; line-height: 1.45; background-color: #f7f7f7; border: 1px solid #ccc; -webkit-border-radius: 3px; border-radius: 3px; -moz-box-shadow: 0 1px 0 rgba(0, 0, 0, 0.2), 0 0 0 0.1em white inset; -webkit-box-shadow: 0 1px 0 rgba(0, 0, 0, 0.2), 0 0 0 0.1em white inset; box-shadow: 0 1px 0 rgba(0, 0, 0, 0.2), 0 0 0 0.1em white inset; margin: 0 0.15em; padding: 0.2em 0.5em; vertical-align: middle; position: relative; top: -0.1em; white-space: nowrap; }

.keyseq kbd:first-child { margin-left: 0; }

.keyseq kbd:last-child { margin-right: 0; }

.menuseq, .menuref { color: #000; }

.menuseq b:not(.caret), .menuref { font-weight: inherit; }

.menuseq { word-spacing: -0.02em; }
.menuseq b.caret { font-size: 1.25em; line-height: 0.8; }
.menuseq i.caret { font-weight: bold; text-align: center; width: 0.45em; }

b.button:before, b.button:after { position: relative; top: -1px; font-weight: normal; }

b.button:before { content: "["; padding: 0 3px 0 2px; }

b.button:after { content: "]"; padding: 0 2px 0 3px; }

#header, #content, #footnotes, #footer { width: 100%; margin-left: auto; margin-right: auto; margin-top: 0; margin-bottom: 0; max-width: 62.5em; *zoom: 1; position: relative; padding-left: 1.5em; padding-right: 1.5em; }
#header:before, #header:after, #content:before, #content:after, #footnotes:before, #footnotes:after, #footer:before, #footer:after { content: " "; display: table; }
#header:after, #content:after, #footnotes:after, #footer:after { clear: both; }

#content { margin-top: 1.25em; }

#content:before { content: none; }

#header > h1:first-child { color: black; margin-top: 2.25rem; margin-bottom: 0; }
#header > h1:first-child + #toc { margin-top: 8px; border-top: 1px solid #ddd; }
#header > h1:only-child, body.toc2 #header > h1:nth-last-child(2) { border-bottom: 1px solid #ddd; padding-bottom: 8px; }
#header .details { border-bottom: 1px solid #ddd; line-height: 1.45; padding-top: 0.25em; padding-bottom: 0.25em; padding-left: 0.25em; color: #365E7A; display: -ms-flexbox; display: -webkit-flex; display: flex; -ms-flex-flow: row wrap; -webkit-flex-flow: row wrap; flex-flow: row wrap; }
#header .details span:first-child { margin-left: -0.125em; }
#header .details span.email a { color: #333; }
#header .details br { display: none; }
#header .details br + span:before { content: "\00a0\2013\00a0"; }
#header .details br + span.author:before { content: "\00a0\22c5\00a0"; color: #333; }
#header .details br + span#revremark:before { content: "\00a0|\00a0"; }
#header #revnumber { text-transform: capitalize; }
#header #revnumber:after { content: "\00a0"; }

#content > h1:first-child:not([class]) { color: black; border-bottom: 1px solid #ddd; padding-bottom: 8px; margin-top: 0; padding-top: 1rem; margin-bottom: 1.25rem; }

#toc { border-bottom: 0 solid #ddd; padding-bottom: 0.5em; }
#toc > ul { margin-left: 0.125em; }
#toc ul.sectlevel0 > li > a { font-style: italic; }
#toc ul.sectlevel0 ul.sectlevel1 { margin: 0.5em 0; }
#toc ul { font-family: Noto, sans-serif; list-style-type: none; }
#toc li { line-height: 1.3334; margin-top: 0.3334em; }
#toc a { text-decoration: none; }
#toc a:active { text-decoration: underline; }

#toctitle { color: black; font-size: 1.2em; }

@media only screen and (min-width: 768px) { #toctitle { font-size: 1.375em; }
  body.toc2 { padding-left: 15em; padding-right: 0; }
  #toc.toc2 { margin-top: 0 !important; background-color: #fff; position: fixed; width: 15em; left: 0; top: 0; border-right: 1px solid #ddd; border-top-width: 0 !important; border-bottom-width: 0 !important; z-index: 1000; padding: 1.25em 1em; height: 100%; overflow: auto; }
  #toc.toc2 #toctitle { margin-top: 0; margin-bottom: 0.8rem; font-size: 1.2em; }
  #toc.toc2 > ul { font-size: 0.9em; margin-bottom: 0; }
  #toc.toc2 ul ul { margin-left: 0; padding-left: 1em; }
  #toc.toc2 ul.sectlevel0 ul.sectlevel1 { padding-left: 0; margin-top: 0.5em; margin-bottom: 0.5em; }
  body.toc2.toc-right { padding-left: 0; padding-right: 15em; }
  body.toc2.toc-right #toc.toc2 { border-right-width: 0; border-left: 1px solid #ddd; left: auto; right: 0; } }
@media only screen and (min-width: 1280px) { body.toc2 { padding-left: 20em; padding-right: 0; }
  #toc.toc2 { width: 20em; }
  #toc.toc2 #toctitle { font-size: 1.375em; }
  #toc.toc2 > ul { font-size: 0.95em; }
  #toc.toc2 ul ul { padding-left: 1.25em; }
  body.toc2.toc-right { padding-left: 0; padding-right: 20em; } }
#content #toc { border-style: solid; border-width: 1px; border-color: #e6e6e6; margin-bottom: 1.25em; padding: 1.25em; background: #fff; -webkit-border-radius: 0; border-radius: 0; }
#content #toc > :first-child { margin-top: 0; }
#content #toc > :last-child { margin-bottom: 0; }

#footer { max-width: 100%; background: none; padding: 1.25em; }

#footer-text { color: black; line-height: 1.44; }

#content { margin-bottom: 0.625em; }

.sect1 { padding-bottom: 0.625em; }

@media only screen and (min-width: 768px) { #content { margin-bottom: 1.25em; }
  .sect1 { padding-bottom: 1.25em; } }
.sect1:last-child { padding-bottom: 0; }

.sect1 + .sect1 { border-top: 0 solid #ddd; }

#content h1 > a.anchor, h2 > a.anchor, h3 > a.anchor, #toctitle > a.anchor, .sidebarblock > .content > .title > a.anchor, h4 > a.anchor, h5 > a.anchor, h6 > a.anchor { position: absolute; z-index: 1001; width: 1.5ex; margin-left: -1.5ex; display: block; text-decoration: none !important; visibility: hidden; text-align: center; font-weight: normal; }
#content h1 > a.anchor:before, h2 > a.anchor:before, h3 > a.anchor:before, #toctitle > a.anchor:before, .sidebarblock > .content > .title > a.anchor:before, h4 > a.anchor:before, h5 > a.anchor:before, h6 > a.anchor:before { content: "\00A7"; font-size: 0.85em; display: block; padding-top: 0.1em; }
#content h1:hover > a.anchor, #content h1 > a.anchor:hover, h2:hover > a.anchor, h2 > a.anchor:hover, h3:hover > a.anchor, #toctitle:hover > a.anchor, .sidebarblock > .content > .title:hover > a.anchor, h3 > a.anchor:hover, #toctitle > a.anchor:hover, .sidebarblock > .content > .title > a.anchor:hover, h4:hover > a.anchor, h4 > a.anchor:hover, h5:hover > a.anchor, h5 > a.anchor:hover, h6:hover > a.anchor, h6 > a.anchor:hover { visibility: visible; }
#content h1 > a.link, h2 > a.link, h3 > a.link, #toctitle > a.link, .sidebarblock > .content > .title > a.link, h4 > a.link, h5 > a.link, h6 > a.link { color: black; text-decoration: none; }
#content h1 > a.link:hover, h2 > a.link:hover, h3 > a.link:hover, #toctitle > a.link:hover, .sidebarblock > .content > .title > a.link:hover, h4 > a.link:hover, h5 > a.link:hover, h6 > a.link:hover { color: black; }

.audioblock, .imageblock, .literalblock, .listingblock, .stemblock, .videoblock { margin-bottom: 1.25em; }

.admonitionblock td.content > .title, .audioblock > .title, .exampleblock > .title, .imageblock > .title, .listingblock > .title, .literalblock > .title, .stemblock > .title, .openblock > .title, .paragraph > .title, .quoteblock > .title, table.tableblock > .title, .verseblock > .title, .videoblock > .title, .dlist > .title, .olist > .title, .ulist > .title, .qlist > .title, .hdlist > .title { text-rendering: optimizeLegibility; text-align: left; }

table.tableblock > caption.title { white-space: nowrap; overflow: visible; max-width: 0; }

.paragraph.lead > p, #preamble > .sectionbody > .paragraph:first-of-type p { color: black; }

table.tableblock #preamble > .sectionbody > .paragraph:first-of-type p { font-size: inherit; }

.admonitionblock > table { border-collapse: separate; border: 0; background: none; width: 100%; }
.admonitionblock > table td.icon { text-align: center; width: 80px; }
.admonitionblock > table td.icon img { max-width: initial; }
.admonitionblock > table td.icon .title { font-weight: bold; font-family: Noto, sans-serif; text-transform: uppercase; }
.admonitionblock > table td.content { padding-left: 1.125em; padding-right: 1.25em; border-left: 1px solid #ddd; color: #365E7A; }
.admonitionblock > table td.content > :last-child > :last-child { margin-bottom: 0; }

.exampleblock > .content { border-style: solid; border-width: 1px; border-color: #e6e6e6; margin-bottom: 1.25em; padding: 1.25em; background: #fff; -webkit-border-radius: 0; border-radius: 0; }
.exampleblock > .content > :first-child { margin-top: 0; }
.exampleblock > .content > :last-child { margin-bottom: 0; }

.sidebarblock { border-style: solid; border-width: 1px; border-color: #e6e6e6; margin-bottom: 1.25em; padding: 1.25em; background: #fff; -webkit-border-radius: 0; border-radius: 0; }
.sidebarblock > :first-child { margin-top: 0; }
.sidebarblock > :last-child { margin-bottom: 0; }
.sidebarblock > .content > .title { color: black; margin-top: 0; }

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<body class="manpage">
<div id="header">
<h1>restrictions(3) Manual Page</h1>
<h2 id="_name">Name</h2>
<div class="sectionbody">
<p>restrictions - Restrictions</p>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_description"><a class="anchor" href="#_description"></a>Description</h2>
<div class="sectionbody">
<div class="olist loweralpha">
<ol class="loweralpha" type="a">
<li>
<p>The use of pointers is somewhat restricted.
The following rules apply:</p>
<div class="ulist">
<ul>
<li>
<p>Arguments to kernel functions declared in a program that are pointers
must be declared with the <code>__global</code>, <code>__constant</code> or <code>__local</code>
qualifier.</p>
</li>
<li>
<p>A pointer declared with the <code>__constant</code> qualifier can only be
assigned to a pointer declared with the <code>__constant</code> qualifier
respectively.</p>
</li>
<li>
<p>Pointers to functions are not allowed.</p>
</li>
<li>
<p>Arguments to kernel functions in a program cannot be
declared as a pointer to a pointer(s).
Variables inside a function or arguments to non-kernel functions in a
program can be declared as a pointer to a pointer(s).
This restriction only applies to OpenCL C 1.2 or below.</p>
</li>
</ul>
</div>
</li>
<li>
<p>An image type (<code>image2d_t</code>, <code>image3d_t</code>, <code>image2d_array_t</code>, <code>image1d_t</code>,
<code>image1d_buffer_t</code> or <code>image1d_array_t</code>) can only be used as the type of
a function argument.
An image function argument cannot be modified.
Elements of an image can only be accessed using the built-in
<a href="https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_C.html#image-read-and-write-functions" target="_blank" rel="noopener">image read and write functions</a>.</p>
<div class="paragraph">
<p>An image type cannot be used to declare a variable, a structure or union
field, an array of images, a pointer to an image, or the return type of a
function.
An image type cannot be used with the <code>__global</code>, <code>__private</code>,
<code>__local</code> and <code>__constant</code> address space qualifiers.</p>
</div>
<div class="paragraph">
<p>The sampler type (<code>sampler_t</code>) can only be used as the type of a function
argument or a variable declared in the program scope or the outermost scope
of a kernel function.
The behavior of a sampler variable declared in a non-outermost scope of a
kernel function is implementation-defined.
A sampler argument or variable cannot be modified.</p>
</div>
<div class="paragraph">
<p>The sampler type cannot be used to declare a structure or union field, an
array of samplers, a pointer to a sampler, or the return type of a function.
The sampler type cannot be used with the <code>__local</code> and <code>__global</code>
address space qualifiers.</p>
</div>
</li>
<li>
<p><a id="restrictions-bitfield"></a> Bit-field struct members are currently not
supported.</p>
</li>
<li>
<p><a id="restrictions-variable-length"></a> Variable length arrays and structures
with flexible (or unsized) arrays are not supported.</p>
</li>
<li>
<p>Variadic functions are not supported, with the exception of <code>printf</code> and
<code>enqueue_kernel</code>.</p>
</li>
<li>
<p>Variadic macros are not supported.
This restriction only applies to OpenCL C 2.0 or below.</p>
</li>
<li>
<p>If a list of parameters in a function declaration is empty, the function
takes no arguments. This is due to the above restriction on variadic
functions.</p>
</li>
<li>
<p>Unless defined in the OpenCL specification, the library functions,
macros, types, and constants defined in the C99 standard headers
<code>assert.h</code>, <code>ctype.h</code>, <code>complex.h</code>, <code>errno.h</code>, <code>fenv.h</code>, <code>float.h</code>,
<code>inttypes.h</code>, <code>limits.h</code>, <code>locale.h</code>, <code>setjmp.h</code>, <code>signal.h</code>,
<code>stdarg.h</code>, <code>stdio.h</code>, <code>stdlib.h</code>, <code>string.h</code>, <code>tgmath.h</code>, <code>time.h</code>,
<code>wchar.h</code> and <code>wctype.h</code> are not available and cannot be included by a
program.</p>
</li>
<li>
<p>The <code>auto</code> and <code>register</code> storage-class specifiers are not supported.</p>
</li>
<li>
<p>Predefined identifiers are not supported.
This restriction only applies to OpenCL C 1.1 or below.</p>
</li>
<li>
<p>Recursion is not supported.</p>
</li>
<li>
<p>The return type of a kernel function must be <code>void</code>.</p>
</li>
<li>
<p>Arguments to kernel functions in a program cannot be declared with the
built-in scalar types <code>bool</code>, <code>size_t</code>, <code>ptrdiff_t</code>, <code>intptr_t</code>, and
<code>uintptr_t</code> or a struct and/or union that contain fields declared to be
one of these built-in scalar types.</p>
</li>
<li>
<p><code>half</code> is not supported as <code>half</code> can be used as a storage format
<sup class="footnote">[<a id="_footnoteref_1" class="footnote" href="#_footnotedef_1" title="View footnote.">1</a>]</sup> only and is not a data type on which
floating-point arithmetic can be performed.</p>
</li>
<li>
<p>Whether or not irreducible control flow is illegal is implementation
defined.</p>
</li>
<li>
<p>The following restriction only applies to
OpenCL C 1.0, and only if the <code>cl_khr_<wbr>byte_<wbr>addressable_<wbr>store</code>
extension macro is not supported:<br>
Built-in types that are less than 32-bits in size, i.e.
<code>char</code>, <code>uchar</code>, <code>char2</code>, <code>uchar2</code>, <code>short</code>, <code>ushort</code>, and <code>half</code>, have
the following restriction:</p>
<div class="ulist">
<ul>
<li>
<p>Writes to a pointer (or arrays) of type <code>char</code>,
<code>uchar</code>, <code>char2</code>, <code>uchar2</code>, <code>short</code>, <code>ushort</code>, and <code>half</code> or to
elements of a struct that are of type <code>char</code>, <code>uchar</code>, <code>char2</code>,
<code>uchar2</code>, <code>short</code> and <code>ushort</code> are not supported.
Refer to <em>section 9.9</em> for additional information.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The kernel example below shows what memory operations are not supported on
built-in types less than 32-bits in size.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-opencl_c" data-lang="opencl_c">kernel void
do_proc (__global char *pA, short b,
         __global short *pB)
{
    char x[100];
    __private char *px = x;
    int id = (int)get_global_id(0);
    short f;

    f = pB[id] + b; // is allowed
    px[1] = pA[1]; // error. px cannot be written.
    pB[id] = b; // error. pB cannot be written
}</code></pre>
</div>
</div>
</li>
<li>
<p>The type qualifiers <code>const</code>, <code>restrict</code> and <code>volatile</code> as defined by the
C99 specification are supported.
These qualifiers cannot be used with <code>image2d_t</code>, <code>image3d_t</code>,
<code>image2d_array_t</code>, <code>image2d_depth_t</code>, <code>image2d_array_depth_t</code>,
<code>image1d_t</code>, <code>image1d_buffer_t</code> and <code>image1d_array_t</code> types.
Types other than pointer types shall not use the <code>restrict</code> qualifier.</p>
</li>
<li>
<p>The event type (<code>event_t</code>) cannot be used as the type of a kernel
function argument.
The event type cannot be used to declare a program scope variable.
The event type cannot be used to declare a structure or union field.
The event type cannot be used with the <code>__local</code>, <code>__constant</code> and
<code>__global</code> address space qualifiers.</p>
</li>
<li>
<p>The <code>clk_event_t</code>, <code>ndrange_t</code> and <code>reserve_id_t</code> types cannot be used
as arguments to kernel functions that get enqueued from the host.
The <code>clk_event_t</code> and <code>reserve_id_t</code> types cannot be declared in program
scope.</p>
</li>
<li>
<p>Kernels enqueued by the host must continue to have their arguments that
are a pointer to a type declared to point to a named address space.</p>
</li>
<li>
<p>A function in an OpenCL program cannot be called <code>main</code>.</p>
</li>
<li>
<p>Implicit function declaration is not supported.</p>
</li>
<li>
<p>Program scope variables can be defined with any valid OpenCL C data type
except for those in <a href="https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_C.html#table-other-builtin-types" target="_blank" rel="noopener">Other Built-in Data Types</a>.
Such program scope variables may be of any user-defined type, or a pointer
to a user-defined type.</p>
<div class="paragraph">
<p>In the presence of shared virtual memory, these pointers or pointer
members should work as expected as long as they are shared virtual memory
pointers and the referenced storage has been mapped appropriately.
Program scope variables can be declared with <code>__constant</code> address space
qualifiers or if <code>__opencl_c_<wbr>program_<wbr>scope_<wbr>global_<wbr>variables</code> feature is
supported with <code>__global</code> address space qualifier.</p>
</div>
</li>
</ol>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also"><a class="anchor" href="#_see_also"></a>See Also</h2>
<div class="sectionbody">
<div class="paragraph">
<p>No cross-references are available</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_document_notes"><a class="anchor" href="#_document_notes"></a>Document Notes</h2>
<div class="sectionbody">
<div class="paragraph">
<p>For more information, see the <a href="https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_C.html#restrictions" target="_blank" rel="noopener">OpenCL C Specification</a></p>
</div>
<div class="paragraph">
<p>This page is extracted from the OpenCL C Specification.
Fixes and changes should be made to the Specification, not directly.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_copyright"><a class="anchor" href="#_copyright"></a>Copyright</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Copyright 2014-2024 The Khronos Group Inc.</p>
</div>
<div class="paragraph">
<p>SPDX-License-Identifier: CC-BY-4.0</p>
</div>
</div>
</div>
</div>
<div id="footnotes">
<hr>
<div class="footnote" id="_footnotedef_1">
<a href="#_footnoteref_1">1</a>. Unless the <code>cl_khr_<wbr>fp16</code> extension is supported and has been enabled.
</div>
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