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Filter: Describe sanitization flags in constant page
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‎reference/filter/book.xml

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<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<book xml:id="book.filter" xmlns="http://docbook.org/ns/docbook">
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<?phpdoc extension-membership="bundled" ?>
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<title>Data Filtering</title>
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<titleabbrev>Filter</titleabbrev>
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<preface xml:id="intro.filter">
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&reftitle.intro;
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<para>
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This extension filters data by either validating or sanitizing it. This is
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especially useful when the data source contains unknown (or foreign) data,
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like user supplied input. For example, this data may come from an HTML form.
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</para>
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<para>
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<simpara>
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This extension provides filters which can be used to validate or sanitize data.
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This is especially useful when the data source contains unknown (or foreign) data,
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like user supplied input.
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For example, this data may come from an <acronym>HTML</acronym> form.
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</simpara>
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<simpara>
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There are two main types of filtering:
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<emphasis>validation</emphasis> and <emphasis>sanitization</emphasis>.
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</para>
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<para>
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Validation is used to
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validate or check if the data meets certain qualifications. For example,
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passing in <constant>FILTER_VALIDATE_EMAIL</constant> will determine if
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the data is a valid email address, but will not change the data itself.
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</para>
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<para>
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<link linkend="filter.filters.sanitize">Sanitization</link> will
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sanitize the data, so it may alter it by removing undesired characters.
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For example, passing in <constant>FILTER_SANITIZE_EMAIL</constant> will
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</simpara>
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<simpara>
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A validation filter is used to check if the data meets certain criteria.
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These filters are identified by the
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<constant>FILTER_VALIDATE_<replaceable>*</replaceable></constant>
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constants.
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For example, the <constant>FILTER_VALIDATE_EMAIL</constant> filter
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can be used to determine if the data is a valid email address.
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However, it will never alter the input data.
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</simpara>
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<simpara>
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Sanitization on the other hand will "clean up" the data,
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therefore it may alter the input data by adding or removing characters.
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These filters are identified by the
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<constant>FILTER_SANITIZE_<replaceable>*</replaceable></constant>
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constants.
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For example, the <constant>FILTER_SANITIZE_EMAIL</constant> filter will
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remove characters that are inappropriate for an email address to contain.
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That said, it does not validate the data.
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</para>
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<para>
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<emphasis>Flags</emphasis> are optionally used with both validation and
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sanitization to tweak behaviour according to need. For example, passing
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in <constant>FILTER_FLAG_PATH_REQUIRED</constant> while filtering an
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<acronym>URL</acronym> will require a path (like <literal>/foo</literal>
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in <literal>http://example.org/foo</literal>) to be present.
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</para>
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However, the sanitized data is not validated to check if it is a valid
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email address.
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</simpara>
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<simpara>
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Most filters support optional <emphasis>flags</emphasis> that can tweak
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the behavior of the filter.
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These flags are identified by the
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<constant>FILTER_FLAG_<replaceable>*</replaceable></constant>
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constants.
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For example, using the <constant>FILTER_FLAG_PATH_REQUIRED</constant> with
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the <constant>FILTER_VALIDATE_URL</constant> validation filter
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requires that the <acronym>URL</acronym> has a path
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(e.g. <literal>/foo</literal> in <literal>https://example.org/foo</literal>).
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</simpara>
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</preface>
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&reference.filter.setup;
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&reference.filter.reference;
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</book>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml

‎reference/filter/constants.xml

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</term>
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<listitem>
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<simpara>
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ID of "unsafe_raw" filter.
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This filter does nothing.
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</simpara>
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<simpara>
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However, it can strip or encode special characters if used together with
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the <constant>FILTER_FLAG_STRIP_<replaceable>*</replaceable></constant>
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and <constant>FILTER_FLAG_ENCODE_<replaceable>*</replaceable></constant>
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filter sanitization flags.
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</simpara>
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</listitem>
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</varlistentry>
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</term>
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<listitem>
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<simpara>
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ID of "string" filter.
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(<emphasis>Deprecated</emphasis> as of PHP 8.1.0,
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use <function>htmlspecialchars</function> instead.)
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This filter strips tags and HTML-encodes double and single quotes.
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</simpara>
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<simpara>
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Optionally it can strip or encode specified characters if used together with
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the <constant>FILTER_FLAG_STRIP_<replaceable>*</replaceable></constant>
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and <constant>FILTER_FLAG_ENCODE_<replaceable>*</replaceable></constant>
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filter sanitization flags.
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</simpara>
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<simpara>
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The behaviour of encoding quotes can be disabled by using the
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<constant>FILTER_FLAG_NO_ENCODE_QUOTES</constant> filter flag.
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</simpara>
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<warning>
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<simpara>
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<emphasis>Deprecated</emphasis> as of PHP 8.1.0,
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use <function>htmlspecialchars</function> instead.
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</simpara>
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</warning>
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</listitem>
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</varlistentry>
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<varlistentry xml:id="constant.filter-sanitize-stripped">
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</term>
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<listitem>
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<simpara>
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ID of "encoded" filter.
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This filter URL-encodes a string.
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</simpara>
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<simpara>
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Optionally it can strip or encode specified characters if used together with
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the <constant>FILTER_FLAG_STRIP_<replaceable>*</replaceable></constant>
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and <constant>FILTER_FLAG_ENCODE_<replaceable>*</replaceable></constant>
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filter sanitization flags.
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</simpara>
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</listitem>
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</varlistentry>
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(<type>int</type>)
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</term>
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<listitem>
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<para>
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This filter HTML-encodes
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<simplelist type="inline">
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<member><literal>'</literal></member>
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<member><literal>"</literal></member>
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<member><literal>&lt;</literal></member>
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<member><literal>&gt;</literal></member>
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<member><literal>&amp;</literal></member>
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</simplelist>
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and characters with an ASCII value less than 32.
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</para>
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<simpara>
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ID of "special_chars" filter.
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Optionally it can strip specified characters if used together with
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the <constant>FILTER_FLAG_STRIP_<replaceable>*</replaceable></constant>
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filter sanitization flags, and it can encode characters with ASCII value
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greater than 127 using <constant>FILTER_FLAG_ENCODE_HIGH</constant>.
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</simpara>
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</listitem>
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</varlistentry>
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</term>
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<listitem>
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<simpara>
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ID of "full_special_chars" filter.
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This filter is equivalent to calling <function>htmlspecialchars</function>
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with <constant>ENT_QUOTES</constant> set.
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</simpara>
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<simpara>
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The behaviour of encoding quotes can be disabled by using the
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<constant>FILTER_FLAG_NO_ENCODE_QUOTES</constant> filter flag.
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</simpara>
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<warning>
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<simpara>
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Like <function>htmlspecialchars</function>, this filter is aware of the
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<link linkend="ini.default-charset">default_charset</link> INI setting.
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If a sequence of bytes is detected that makes up an invalid character
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in the current character set then the entire string is rejected
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resulting in a empty string being returned.
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</simpara>
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</warning>
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</listitem>
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</varlistentry>
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<varlistentry xml:id="constant.filter-sanitize-email">

‎reference/filter/filters.xml

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<chapter xml:id="filter.filters" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Types of filters</title>
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<!-- Sanitize filters: {{{-->
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<section xml:id="filter.filters.sanitize">
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<title>Sanitize filters</title>
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<para>
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<table>
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<title>List of filters for sanitization</title>
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<tgroup cols="5">
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<thead>
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<row>
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<entry>ID</entry>
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<entry>Name</entry>
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<entry>Flags</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><constant>FILTER_SANITIZE_ENCODED</constant></entry>
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<entry>"encoded"</entry>
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<entry>
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<constant>FILTER_FLAG_STRIP_LOW</constant>,
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<constant>FILTER_FLAG_STRIP_HIGH</constant>,
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<constant>FILTER_FLAG_STRIP_BACKTICK</constant>,
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<constant>FILTER_FLAG_ENCODE_LOW</constant>,
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<constant>FILTER_FLAG_ENCODE_HIGH</constant>
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</entry>
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<entry>URL-encode string, optionally strip or encode special characters.</entry>
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</row>
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<row>
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<entry><constant>FILTER_SANITIZE_SPECIAL_CHARS</constant></entry>
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<entry>"special_chars"</entry>
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<entry>
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<constant>FILTER_FLAG_STRIP_LOW</constant>,
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<constant>FILTER_FLAG_STRIP_HIGH</constant>,
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<constant>FILTER_FLAG_STRIP_BACKTICK</constant>,
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<constant>FILTER_FLAG_ENCODE_HIGH</constant>
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</entry>
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<entry>
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HTML-encode <literal>'"&lt;&gt;&amp;</literal> and characters with
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ASCII value less than 32, optionally strip or encode other special
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characters.
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</entry>
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</row>
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<row>
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<entry><constant>FILTER_SANITIZE_FULL_SPECIAL_CHARS</constant></entry>
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<entry>"full_special_chars"</entry>
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<entry>
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<constant>FILTER_FLAG_NO_ENCODE_QUOTES</constant>
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</entry>
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<entry>
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Equivalent to calling <function>htmlspecialchars</function> with <constant>ENT_QUOTES</constant> set. Encoding quotes can
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be disabled by setting <constant>FILTER_FLAG_NO_ENCODE_QUOTES</constant>. Like <function>htmlspecialchars</function>, this
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filter is aware of the <link linkend="ini.default-charset">default_charset</link> and if a sequence of bytes is detected that
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makes up an invalid character in the current character set then the entire string is rejected resulting in a 0-length string.
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When using this filter as a default filter, see the warning below about setting the default flags to 0.
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</entry>
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</row>
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<row>
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<entry><constant>FILTER_SANITIZE_STRING</constant></entry>
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<entry>"string"</entry>
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<entry>
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<constant>FILTER_FLAG_NO_ENCODE_QUOTES</constant>,
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<constant>FILTER_FLAG_STRIP_LOW</constant>,
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<constant>FILTER_FLAG_STRIP_HIGH</constant>,
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<constant>FILTER_FLAG_STRIP_BACKTICK</constant>,
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<constant>FILTER_FLAG_ENCODE_LOW</constant>,
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<constant>FILTER_FLAG_ENCODE_HIGH</constant>,
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<constant>FILTER_FLAG_ENCODE_AMP</constant>
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</entry>
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<entry>
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Strip tags and HTML-encode double and single quotes, optionally strip
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or encode special characters. Encoding quotes can be
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disabled by setting <constant>FILTER_FLAG_NO_ENCODE_QUOTES</constant>.
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(<emphasis>Deprecated</emphasis> as of PHP 8.1.0,
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use <function>htmlspecialchars</function> instead.)
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</entry>
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</row>
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<row>
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<entry><constant>FILTER_UNSAFE_RAW</constant></entry>
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<entry>"unsafe_raw"</entry>
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<entry>
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<constant>FILTER_FLAG_STRIP_LOW</constant>,
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<constant>FILTER_FLAG_STRIP_HIGH</constant>,
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<constant>FILTER_FLAG_STRIP_BACKTICK</constant>,
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<constant>FILTER_FLAG_ENCODE_LOW</constant>,
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<constant>FILTER_FLAG_ENCODE_HIGH</constant>,
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<constant>FILTER_FLAG_ENCODE_AMP</constant>
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</entry>
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<entry>
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Do nothing, optionally strip or encode special characters. This
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filter is also aliased to <constant>FILTER_DEFAULT</constant>.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</para>
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<simplesect role="changelog">
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&reftitle.changelog;
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<para>
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>&Version;</entry>
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<entry>&Description;</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>8.1.0</entry>
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<entry>
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<constant>FILTER_SANITIZE_STRING</constant> and
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<constant>FILTER_SANITIZE_STRIPPED</constant> have been deprecated.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</para>
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</simplesect>
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</section>
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<!--}}}-->
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<!-- Filter flags: {{{-->
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<section xml:id="filter.filters.flags">
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<title>Filter flags</title>

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