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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>12.8 Syntax Taints</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.css" title="default"/><link rel="stylesheet" type="text/css" href="icons.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Reference</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewselflink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr
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use as either a binding or expression. If a syntax object <span class="RktVar">stx</span> is
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<a href="stxcerts.html#%28tech._tainted%29" class="techoutside" data-pltdoc="x"><span class="techinside">tainted</span></a>, then any syntax object in the result of
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<span class="RktPn">(</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax-e%29%29" class="RktValLink" data-pltdoc="x">syntax-e</a></span><span class="stt"> </span><span class="RktVar">stx</span><span class="RktPn">)</span> is <a href="stxcerts.html#%28tech._tainted%29" class="techoutside" data-pltdoc="x"><span class="techinside">tainted</span></a>, and <span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._datum-~3esyntax%29%29" class="RktValLink" data-pltdoc="x">datum->syntax</a></span>
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with <span class="RktVar">stx</span> as its first argument produces a <a href="stxcerts.html#%28tech._tainted%29" class="techoutside" data-pltdoc="x"><span class="techinside">tainted</span></a>
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syntax object. Any syntax object in the result of <span class="RktPn">(</span><span class="RktSym"><a href="stxprops.html#%28def._%28%28quote._~23~25kernel%29._syntax-property%29%29" class="RktValLink" data-pltdoc="x">syntax-property</a></span><span class="stt"> </span><span class="RktVar">stx</span><span class="stt"> </span><span class="RktVar">key</span><span class="RktPn">)</span>
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is also tainted if it is in a position within the value that would be
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reached by <span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._datum-~3esyntax%29%29" class="RktValLink" data-pltdoc="x">datum->syntax</a></span>’s conversion. Taints cannot be removed.</p><p>A syntax object is tainted when it is included in an exception by the
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macro expander or when it is produced by a function like
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<span class="RktSym"><a href="Expanding_Top-Level_Forms.html#%28def._%28%28quote._~23~25kernel%29._expand%29%29" class="RktValLink" data-pltdoc="x">expand</a></span> using a <a href="modprotect.html#%28tech._code._inspector%29" class="techoutside" data-pltdoc="x"><span class="techinside">code inspector</span></a> that is not the original
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code inspector. The function <span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-taint%29%29" class="RktValLink" data-pltdoc="x">syntax-taint</a></span> also returns a
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tainted syntax object.</p><p>Previous versions of Racket included a notion of <span style="font-style: italic">arming</span> and
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<span style="font-style: italic">disarming</span> syntax to trigger taints or avoid taints. That
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indirection is no longer supported, and the operations
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<span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-arm%29%29" class="RktValLink" data-pltdoc="x">syntax-arm</a></span>, <span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-disarm%29%29" class="RktValLink" data-pltdoc="x">syntax-disarm</a></span>, <span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-rearm%29%29" class="RktValLink" data-pltdoc="x">syntax-rearm</a></span>, and
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<span class="RktSym"><a href="stxcerts.html#%28def._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._syntax-protect%29%29" class="RktValLink" data-pltdoc="x">syntax-protect</a></span> now have no effect on their arguments. Along
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similar lines, the syntax properties (see <a href="stxprops.html" data-pltdoc="x">Syntax Object Properties</a>)
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<a name="(idx._(gentag._239._(lib._scribblings/reference/reference..scrbl)))"></a><span class="RktVal">'</span><span class="RktVal">taint-mode</span> and <a name="(idx._(gentag._240._(lib._scribblings/reference/reference..scrbl)))"></a><span class="RktVal">'</span><span class="RktVal">certify-mode</span> were
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formerly used to control syntax arming and are no longer specifically
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recognized by the macro expander.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._syntax-tainted~3f))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-tainted~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">syntax-tainted?</a></span></span><span class="hspace"> </span><span class="RktVar">stx</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktVar">stx</span> is <a href="stxcerts.html#%28tech._tainted%29" class="techoutside" data-pltdoc="x"><span class="techinside">tainted</span></a>, <span class="RktVal">#f</span>
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otherwise.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._syntax-arm))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-arm%29%29" class="RktValDef RktValLink" data-pltdoc="x">syntax-arm</a></span></span><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">inspector</span><span class="hspace"> </span><span class="RktVar">use-mode?</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">inspector</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="inspectors.html#%28def._%28%28quote._~23~25kernel%29._inspector~3f%29%29" class="RktValLink" data-pltdoc="x">inspector?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">use-mode?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVar">stx</span>.</div></p><p class="SHistory">Changed in version 8.2.0.4 of package <span class="stt">base</span>: Changed to just return <span class="RktVar">stx</span> instead
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of returning “armed” syntax.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/private/stxcase-scheme..rkt)._syntax-protect))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stxcerts.html#%28def._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._syntax-protect%29%29" class="RktValDef RktValLink" data-pltdoc="x">syntax-protect</a></span></span><span class="hspace"> </span><span class="RktVar">stx</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVar">stx</span>.</div></p><p class="SHistory">Changed in version 8.2.0.4 of package <span class="stt">base</span>: Changed to just return <span class="RktVar">stx</span> instead
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of returning “armed” syntax.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._syntax-disarm))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-disarm%29%29" class="RktValDef RktValLink" data-pltdoc="x">syntax-disarm</a></span></span><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span><span class="RktVar">inspector</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">inspector</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="inspectors.html#%28def._%28%28quote._~23~25kernel%29._inspector~3f%29%29" class="RktValLink" data-pltdoc="x">inspector?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVar">stx</span>.</div></p><p class="SHistory">Changed in version 8.2.0.4 of package <span class="stt">base</span>: Changed to just return <span class="RktVar">stx</span> instead
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of potentially “disarming” syntax.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._syntax-rearm))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-rearm%29%29" class="RktValDef RktValLink" data-pltdoc="x">syntax-rearm</a></span></span><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span><span class="RktVar">from-stx</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">use-mode?</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">from-stx</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">use-mode?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVar">stx</span>.</div></p><p class="SHistory">Changed in version 8.2.0.4 of package <span class="stt">base</span>: Changed to just return <span class="RktVar">stx</span> instead
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of potentially “arming” syntax.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._syntax-taint))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stxcerts.html#%28def._%28%28quote._~23~25kernel%29._syntax-taint%29%29" class="RktValDef RktValLink" data-pltdoc="x">syntax-taint</a></span></span><span class="hspace"> </span><span class="RktVar">stx</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">stx</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <a href="stxcerts.html#%28tech._tainted%29" class="techoutside" data-pltdoc="x"><span class="techinside">tainted</span></a> version of <span class="RktVar">stx</span>, which is <span class="RktVar">stx</span>
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if it is already tainted.</div></p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="stxprops.html" title="backward to "12.7 Syntax Object Properties"" data-pltdoc="x">← prev</a> <a href="Macros.html" title="up to "12 Macros"" data-pltdoc="x">up</a> <a href="Expanding_Top-Level_Forms.html" title="forward to "12.9 Expanding Top-Level Forms"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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