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+= Double Quoted Strings
+
+.Syntax
+`"string"`
+
+A double-quoted string allows escape sequences and xref:xlat/index.adoc[dynamic
+expansions]. As with xref:type/string/single.adoc[single-quoted strings], text
+within double quotes can include spaces.
+
+The main difference between the single and double quoted strings is
+that the double quoted strings can be dynamically expanded. The syntax
+`${...}` is used for parse-time expansion and `%{...}` is used for
+run-time expansion. The difference between the two methods is that the
+`${...}` form is expanded when the server loads the configuration
+files and is valid anywhere in the configuration files. The `%{...}`
+xref:xlat/index.adoc[string expansion] form is valid only in conditional
+expressions and attribute assignments.
+
+The output of the dynamic expansion can be interpreted as a string,
+a number, or an IP address, depending on its context.
+
+Note that the interpretation of text _strongly_ depends on the
+context.  The text `"0000"` can be interpreted as a data type
+"integer", having value zero, or a data type "string", having value
+`"0000"`.  In general when a particular piece of text is used, it is
+used with the context of a known attribute.  That attribute has a
+xref:type/index.adoc[data type], and the text will be interpreted as that
+data type.
+
+NOTE: Most values retrieved from external datastores will be treated implicitly
+as double-quoted strings.
+
+== Escape sequences
+
+Escape sequences allow the inclusion of characters that may be difficult to
+represent in datastores, or the FreeRADIUS configuration files.
+
+.Escape sequences and their descriptions
+[options="header", cols="15%,85%"]
+|=====
+| Escape sequence     | Character represented
+| `\\`                | Literal backslash (0x5c)
+| `\r`                | Carriage return (0x0d)
+| `\n`                | Line feed (0x0a)
+| `\t`                | Horizontal tab (0x09)
+| `\"`                | Double quote (0x22)
+| `\x<hex><hex>`      | A byte whose numerical value is given by `<hex><hex>` interpreted as a hexadecimal number.
+| `\x<oct><oct><oct>` | A byte whose numerical value is given by `<oct><oct><oct>` interpreted as an octal number.
+|=====
+
+.Examples
+
+`"word"` +
+`"a string"' +
+`"foo\"bar\""` +
+`"this is a long string"` +
+`"this has embedded\ncharacters"` +
+`"attribute\tvalue\nusername\t%{User-Name}\nreply-message\t%{reply.Reply-Message}"`
+`"The result of 'SELECT * FROM foo WHERE 1' is: %{sql:SELECT * FROM foo WHERE 1}"`
+
+// Licenced under CC-by-NC 4.0.
+// Copyright (C) 2019 Arran Cudbard-Bell <a.cudbardb@freeradius.org>
+// Copyright (C) 2019 The FreeRADIUS project.
+// Copyright (C) 2020 Network RADIUS SAS.
+
+
+
+