Implemented SoftBreak and new `--wrap` option.

Added threefold wrapping option.

* Command line option: deprecated `--no-wrap`, added
  `--wrap=[auto|none|preserve]`
* Added WrapOption, exported from Text.Pandoc.Options
* Changed type of writerWrapText in WriterOptions from
  Bool to WrapOption.
* Modified Text.Pandoc.Shared functions for SoftBreak.
* Supported SoftBreak in writers.
* Updated tests.
* Updated README.

Closes #1701.

1 files changed, 19 insertions, 19 deletions

diff --git a/tests/writer.native b/tests/writer.native
index 3501fadcb..c887e5467 100644
--- a/tests/writer.native
+++ b/tests/writer.native
@@ -1,5 +1,5 @@
 Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Space,Str "MacFarlane"],MetaInlines [Str "Anonymous"]]),("date",MetaInlines [Str "July",Space,Str "17,",Space,Str "2006"]),("title",MetaInlines [Str "Pandoc",Space,Str "Test",Space,Str "Suite"])]})
-[Para [Str "This",Space,Str "is",Space,Str "a",Space,Str "set",Space,Str "of",Space,Str "tests",Space,Str "for",Space,Str "pandoc.",Space,Str "Most",Space,Str "of",Space,Str "them",Space,Str "are",Space,Str "adapted",Space,Str "from",Space,Str "John",Space,Str "Gruber\8217s",Space,Str "markdown",Space,Str "test",Space,Str "suite."]
+[Para [Str "This",Space,Str "is",Space,Str "a",Space,Str "set",Space,Str "of",Space,Str "tests",Space,Str "for",Space,Str "pandoc.",Space,Str "Most",Space,Str "of",Space,Str "them",Space,Str "are",Space,Str "adapted",Space,Str "from",SoftBreak,Str "John",Space,Str "Gruber\8217s",Space,Str "markdown",Space,Str "test",Space,Str "suite."]
 ,HorizontalRule
 ,Header 1 ("headers",[],[]) [Str "Headers"]
 ,Header 2 ("level-2-with-an-embedded-link",[],[]) [Str "Level",Space,Str "2",Space,Str "with",Space,Str "an",Space,Link ("",[],[]) [Str "embedded",Space,Str "link"] ("/url","")]
@@ -15,14 +15,14 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
 ,HorizontalRule
 ,Header 1 ("paragraphs",[],[]) [Str "Paragraphs"]
 ,Para [Str "Here\8217s",Space,Str "a",Space,Str "regular",Space,Str "paragraph."]
-,Para [Str "In",Space,Str "Markdown",Space,Str "1.0.0",Space,Str "and",Space,Str "earlier.",Space,Str "Version",Space,Str "8.",Space,Str "This",Space,Str "line",Space,Str "turns",Space,Str "into",Space,Str "a",Space,Str "list",Space,Str "item.",Space,Str "Because",Space,Str "a",Space,Str "hard-wrapped",Space,Str "line",Space,Str "in",Space,Str "the",Space,Str "middle",Space,Str "of",Space,Str "a",Space,Str "paragraph",Space,Str "looked",Space,Str "like",Space,Str "a",Space,Str "list",Space,Str "item."]
-,Para [Str "Here\8217s",Space,Str "one",Space,Str "with",Space,Str "a",Space,Str "bullet.",Space,Str "*",Space,Str "criminey."]
+,Para [Str "In",Space,Str "Markdown",Space,Str "1.0.0",Space,Str "and",Space,Str "earlier.",Space,Str "Version",SoftBreak,Str "8.",Space,Str "This",Space,Str "line",Space,Str "turns",Space,Str "into",Space,Str "a",Space,Str "list",Space,Str "item.",SoftBreak,Str "Because",Space,Str "a",Space,Str "hard-wrapped",Space,Str "line",Space,Str "in",Space,Str "the",SoftBreak,Str "middle",Space,Str "of",Space,Str "a",Space,Str "paragraph",Space,Str "looked",Space,Str "like",Space,Str "a",SoftBreak,Str "list",Space,Str "item."]
+,Para [Str "Here\8217s",Space,Str "one",Space,Str "with",Space,Str "a",Space,Str "bullet.",SoftBreak,Str "*",Space,Str "criminey."]
 ,Para [Str "There",Space,Str "should",Space,Str "be",Space,Str "a",Space,Str "hard",Space,Str "line",Space,Str "break",LineBreak,Str "here."]
 ,HorizontalRule
 ,Header 1 ("block-quotes",[],[]) [Str "Block",Space,Str "Quotes"]
 ,Para [Str "E-mail",Space,Str "style:"]
 ,BlockQuote
- [Para [Str "This",Space,Str "is",Space,Str "a",Space,Str "block",Space,Str "quote.",Space,Str "It",Space,Str "is",Space,Str "pretty",Space,Str "short."]]
+ [Para [Str "This",Space,Str "is",Space,Str "a",Space,Str "block",Space,Str "quote.",SoftBreak,Str "It",Space,Str "is",Space,Str "pretty",Space,Str "short."]]
 ,BlockQuote
  [Para [Str "Code",Space,Str "in",Space,Str "a",Space,Str "block",Space,Str "quote:"]
  ,CodeBlock ("",[],[]) "sub status {\n    print \"working\";\n}"
@@ -35,7 +35,7 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
   [Para [Str "nested"]]
  ,BlockQuote
   [Para [Str "nested"]]]
-,Para [Str "This",Space,Str "should",Space,Str "not",Space,Str "be",Space,Str "a",Space,Str "block",Space,Str "quote:",Space,Str "2",Space,Str ">",Space,Str "1."]
+,Para [Str "This",Space,Str "should",Space,Str "not",Space,Str "be",Space,Str "a",Space,Str "block",Space,Str "quote:",Space,Str "2",SoftBreak,Str ">",Space,Str "1."]
 ,Para [Str "And",Space,Str "a",Space,Str "following",Space,Str "paragraph."]
 ,HorizontalRule
 ,Header 1 ("code-blocks",[],[]) [Str "Code",Space,Str "Blocks"]
@@ -100,7 +100,7 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
 ,Para [Str "Multiple",Space,Str "paragraphs:"]
 ,OrderedList (1,Decimal,Period)
  [[Para [Str "Item",Space,Str "1,",Space,Str "graf",Space,Str "one."]
-  ,Para [Str "Item",Space,Str "1.",Space,Str "graf",Space,Str "two.",Space,Str "The",Space,Str "quick",Space,Str "brown",Space,Str "fox",Space,Str "jumped",Space,Str "over",Space,Str "the",Space,Str "lazy",Space,Str "dog\8217s",Space,Str "back."]]
+  ,Para [Str "Item",Space,Str "1.",Space,Str "graf",Space,Str "two.",Space,Str "The",Space,Str "quick",Space,Str "brown",Space,Str "fox",Space,Str "jumped",Space,Str "over",Space,Str "the",Space,Str "lazy",Space,Str "dog\8217s",SoftBreak,Str "back."]]
  ,[Para [Str "Item",Space,Str "2."]]
  ,[Para [Str "Item",Space,Str "3."]]]
 ,Header 2 ("nested",[],[]) [Str "Nested"]
@@ -130,18 +130,18 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
  ,[Para [Str "Third"]]]
 ,Header 2 ("tabs-and-spaces",[],[]) [Str "Tabs",Space,Str "and",Space,Str "spaces"]
 ,BulletList
- [[Para [Str "this",Space,Str "is",Space,Str "a",Space,Str "list",Space,Str "item",Space,Str "indented",Space,Str "with",Space,Str "tabs"]]
- ,[Para [Str "this",Space,Str "is",Space,Str "a",Space,Str "list",Space,Str "item",Space,Str "indented",Space,Str "with",Space,Str "spaces"]
+ [[Para [Str "this",Space,Str "is",Space,Str "a",Space,Str "list",Space,Str "item",SoftBreak,Str "indented",Space,Str "with",Space,Str "tabs"]]
+ ,[Para [Str "this",Space,Str "is",Space,Str "a",Space,Str "list",Space,Str "item",SoftBreak,Str "indented",Space,Str "with",Space,Str "spaces"]
   ,BulletList
-   [[Para [Str "this",Space,Str "is",Space,Str "an",Space,Str "example",Space,Str "list",Space,Str "item",Space,Str "indented",Space,Str "with",Space,Str "tabs"]]
-   ,[Para [Str "this",Space,Str "is",Space,Str "an",Space,Str "example",Space,Str "list",Space,Str "item",Space,Str "indented",Space,Str "with",Space,Str "spaces"]]]]]
+   [[Para [Str "this",Space,Str "is",Space,Str "an",Space,Str "example",Space,Str "list",Space,Str "item",SoftBreak,Str "indented",Space,Str "with",Space,Str "tabs"]]
+   ,[Para [Str "this",Space,Str "is",Space,Str "an",Space,Str "example",Space,Str "list",Space,Str "item",SoftBreak,Str "indented",Space,Str "with",Space,Str "spaces"]]]]]
 ,Header 2 ("fancy-list-markers",[],[]) [Str "Fancy",Space,Str "list",Space,Str "markers"]
 ,OrderedList (2,Decimal,TwoParens)
  [[Plain [Str "begins",Space,Str "with",Space,Str "2"]]
  ,[Para [Str "and",Space,Str "now",Space,Str "3"]
   ,Para [Str "with",Space,Str "a",Space,Str "continuation"]
   ,OrderedList (4,LowerRoman,Period)
-   [[Plain [Str "sublist",Space,Str "with",Space,Str "roman",Space,Str "numerals,",Space,Str "starting",Space,Str "with",Space,Str "4"]]
+   [[Plain [Str "sublist",Space,Str "with",Space,Str "roman",Space,Str "numerals,",SoftBreak,Str "starting",Space,Str "with",Space,Str "4"]]
    ,[Plain [Str "more",Space,Str "items"]
     ,OrderedList (1,UpperAlpha,TwoParens)
      [[Plain [Str "a",Space,Str "subsublist"]]
@@ -194,7 +194,7 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
 ,DefinitionList
  [([Emph [Str "apple"]],
    [[Para [Str "red",Space,Str "fruit"]
-    ,Para [Str "contains",Space,Str "seeds,",Space,Str "crisp,",Space,Str "pleasant",Space,Str "to",Space,Str "taste"]]])
+    ,Para [Str "contains",Space,Str "seeds,",SoftBreak,Str "crisp,",Space,Str "pleasant",Space,Str "to",Space,Str "taste"]]])
  ,([Emph [Str "orange"]],
    [[Para [Str "orange",Space,Str "fruit"]
     ,CodeBlock ("",[],[]) "{ orange code block }"
@@ -260,7 +260,7 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
 ,Div ("",[],[])
  [Div ("",[],[])
   [Div ("",[],[])
-   [Plain [Str "foo"]]]]
+   [Plain [Str "foo",SoftBreak]]]]
 ,Para [Str "This",Space,Str "should",Space,Str "just",Space,Str "be",Space,Str "an",Space,Str "HTML",Space,Str "comment:"]
 ,RawBlock (Format "html") "<!-- Comment -->"
 ,Para [Str "Multiline:"]
@@ -295,13 +295,13 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
 ,Para [Strikeout [Str "This",Space,Str "is",Space,Emph [Str "strikeout"],Str "."]]
 ,Para [Str "Superscripts:",Space,Str "a",Superscript [Str "bc"],Str "d",Space,Str "a",Superscript [Emph [Str "hello"]],Space,Str "a",Superscript [Str "hello\160there"],Str "."]
 ,Para [Str "Subscripts:",Space,Str "H",Subscript [Str "2"],Str "O,",Space,Str "H",Subscript [Str "23"],Str "O,",Space,Str "H",Subscript [Str "many\160of\160them"],Str "O."]
-,Para [Str "These",Space,Str "should",Space,Str "not",Space,Str "be",Space,Str "superscripts",Space,Str "or",Space,Str "subscripts,",Space,Str "because",Space,Str "of",Space,Str "the",Space,Str "unescaped",Space,Str "spaces:",Space,Str "a^b",Space,Str "c^d,",Space,Str "a~b",Space,Str "c~d."]
+,Para [Str "These",Space,Str "should",Space,Str "not",Space,Str "be",Space,Str "superscripts",Space,Str "or",Space,Str "subscripts,",SoftBreak,Str "because",Space,Str "of",Space,Str "the",Space,Str "unescaped",Space,Str "spaces:",Space,Str "a^b",Space,Str "c^d,",Space,Str "a~b",Space,Str "c~d."]
 ,HorizontalRule
 ,Header 1 ("smart-quotes-ellipses-dashes",[],[]) [Str "Smart",Space,Str "quotes,",Space,Str "ellipses,",Space,Str "dashes"]
 ,Para [Quoted DoubleQuote [Str "Hello,"],Space,Str "said",Space,Str "the",Space,Str "spider.",Space,Quoted DoubleQuote [Quoted SingleQuote [Str "Shelob"],Space,Str "is",Space,Str "my",Space,Str "name."]]
 ,Para [Quoted SingleQuote [Str "A"],Str ",",Space,Quoted SingleQuote [Str "B"],Str ",",Space,Str "and",Space,Quoted SingleQuote [Str "C"],Space,Str "are",Space,Str "letters."]
-,Para [Quoted SingleQuote [Str "Oak,"],Space,Quoted SingleQuote [Str "elm,"],Space,Str "and",Space,Quoted SingleQuote [Str "beech"],Space,Str "are",Space,Str "names",Space,Str "of",Space,Str "trees.",Space,Str "So",Space,Str "is",Space,Quoted SingleQuote [Str "pine."]]
-,Para [Quoted SingleQuote [Str "He",Space,Str "said,",Space,Quoted DoubleQuote [Str "I",Space,Str "want",Space,Str "to",Space,Str "go."]],Space,Str "Were",Space,Str "you",Space,Str "alive",Space,Str "in",Space,Str "the",Space,Str "70\8217s?"]
+,Para [Quoted SingleQuote [Str "Oak,"],Space,Quoted SingleQuote [Str "elm,"],Space,Str "and",Space,Quoted SingleQuote [Str "beech"],Space,Str "are",Space,Str "names",Space,Str "of",Space,Str "trees.",SoftBreak,Str "So",Space,Str "is",Space,Quoted SingleQuote [Str "pine."]]
+,Para [Quoted SingleQuote [Str "He",Space,Str "said,",Space,Quoted DoubleQuote [Str "I",Space,Str "want",Space,Str "to",Space,Str "go."]],Space,Str "Were",Space,Str "you",Space,Str "alive",Space,Str "in",Space,Str "the",SoftBreak,Str "70\8217s?"]
 ,Para [Str "Here",Space,Str "is",Space,Str "some",Space,Str "quoted",Space,Quoted SingleQuote [Code ("",[],[]) "code"],Space,Str "and",Space,Str "a",Space,Quoted DoubleQuote [Link ("",[],[]) [Str "quoted",Space,Str "link"] ("http://example.com/?foo=1&bar=2","")],Str "."]
 ,Para [Str "Some",Space,Str "dashes:",Space,Str "one\8212two",Space,Str "\8212",Space,Str "three\8212four",Space,Str "\8212",Space,Str "five."]
 ,Para [Str "Dashes",Space,Str "between",Space,Str "numbers:",Space,Str "5\8211\&7,",Space,Str "255\8211\&66,",Space,Str "1987\8211\&1999."]
@@ -315,12 +315,12 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
  ,[Plain [Math InlineMath "\\alpha \\wedge \\omega"]]
  ,[Plain [Math InlineMath "223"]]
  ,[Plain [Math InlineMath "p",Str "-Tree"]]
- ,[Plain [Str "Here\8217s",Space,Str "some",Space,Str "display",Space,Str "math:",Space,Math DisplayMath "\\frac{d}{dx}f(x)=\\lim_{h\\to 0}\\frac{f(x+h)-f(x)}{h}"]]
+ ,[Plain [Str "Here\8217s",Space,Str "some",Space,Str "display",Space,Str "math:",SoftBreak,Math DisplayMath "\\frac{d}{dx}f(x)=\\lim_{h\\to 0}\\frac{f(x+h)-f(x)}{h}"]]
  ,[Plain [Str "Here\8217s",Space,Str "one",Space,Str "that",Space,Str "has",Space,Str "a",Space,Str "line",Space,Str "break",Space,Str "in",Space,Str "it:",Space,Math InlineMath "\\alpha + \\omega \\times x^2",Str "."]]]
 ,Para [Str "These",Space,Str "shouldn\8217t",Space,Str "be",Space,Str "math:"]
 ,BulletList
  [[Plain [Str "To",Space,Str "get",Space,Str "the",Space,Str "famous",Space,Str "equation,",Space,Str "write",Space,Code ("",[],[]) "$e = mc^2$",Str "."]]
- ,[Plain [Str "$22,000",Space,Str "is",Space,Str "a",Space,Emph [Str "lot"],Space,Str "of",Space,Str "money.",Space,Str "So",Space,Str "is",Space,Str "$34,000.",Space,Str "(It",Space,Str "worked",Space,Str "if",Space,Quoted DoubleQuote [Str "lot"],Space,Str "is",Space,Str "emphasized.)"]]
+ ,[Plain [Str "$22,000",Space,Str "is",Space,Str "a",Space,Emph [Str "lot"],Space,Str "of",Space,Str "money.",Space,Str "So",Space,Str "is",Space,Str "$34,000.",SoftBreak,Str "(It",Space,Str "worked",Space,Str "if",Space,Quoted DoubleQuote [Str "lot"],Space,Str "is",Space,Str "emphasized.)"]]
  ,[Plain [Str "Shoes",Space,Str "($20)",Space,Str "and",Space,Str "socks",Space,Str "($5)."]]
  ,[Plain [Str "Escaped",Space,Code ("",[],[]) "$",Str ":",Space,Str "$73",Space,Emph [Str "this",Space,Str "should",Space,Str "be",Space,Str "emphasized"],Space,Str "23$."]]]
 ,Para [Str "Here\8217s",Space,Str "a",Space,Str "LaTeX",Space,Str "table:"]
@@ -403,7 +403,7 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
 ,Para [Str "Here",Space,Str "is",Space,Str "a",Space,Str "movie",Space,Image ("",[],[]) [Str "movie"] ("movie.jpg",""),Space,Str "icon."]
 ,HorizontalRule
 ,Header 1 ("footnotes",[],[]) [Str "Footnotes"]
-,Para [Str "Here",Space,Str "is",Space,Str "a",Space,Str "footnote",Space,Str "reference,",Note [Para [Str "Here",Space,Str "is",Space,Str "the",Space,Str "footnote.",Space,Str "It",Space,Str "can",Space,Str "go",Space,Str "anywhere",Space,Str "after",Space,Str "the",Space,Str "footnote",Space,Str "reference.",Space,Str "It",Space,Str "need",Space,Str "not",Space,Str "be",Space,Str "placed",Space,Str "at",Space,Str "the",Space,Str "end",Space,Str "of",Space,Str "the",Space,Str "document."]],Space,Str "and",Space,Str "another.",Note [Para [Str "Here\8217s",Space,Str "the",Space,Str "long",Space,Str "note.",Space,Str "This",Space,Str "one",Space,Str "contains",Space,Str "multiple",Space,Str "blocks."],Para [Str "Subsequent",Space,Str "blocks",Space,Str "are",Space,Str "indented",Space,Str "to",Space,Str "show",Space,Str "that",Space,Str "they",Space,Str "belong",Space,Str "to",Space,Str "the",Space,Str "footnote",Space,Str "(as",Space,Str "with",Space,Str "list",Space,Str "items)."],CodeBlock ("",[],[]) "  { <code> }",Para [Str "If",Space,Str "you",Space,Str "want,",Space,Str "you",Space,Str "can",Space,Str "indent",Space,Str "every",Space,Str "line,",Space,Str "but",Space,Str "you",Space,Str "can",Space,Str "also",Space,Str "be",Space,Str "lazy",Space,Str "and",Space,Str "just",Space,Str "indent",Space,Str "the",Space,Str "first",Space,Str "line",Space,Str "of",Space,Str "each",Space,Str "block."]],Space,Str "This",Space,Str "should",Space,Emph [Str "not"],Space,Str "be",Space,Str "a",Space,Str "footnote",Space,Str "reference,",Space,Str "because",Space,Str "it",Space,Str "contains",Space,Str "a",Space,Str "space.[^my",Space,Str "note]",Space,Str "Here",Space,Str "is",Space,Str "an",Space,Str "inline",Space,Str "note.",Note [Para [Str "This",Space,Str "is",Space,Emph [Str "easier"],Space,Str "to",Space,Str "type.",Space,Str "Inline",Space,Str "notes",Space,Str "may",Space,Str "contain",Space,Link ("",[],[]) [Str "links"] ("http://google.com",""),Space,Str "and",Space,Code ("",[],[]) "]",Space,Str "verbatim",Space,Str "characters,",Space,Str "as",Space,Str "well",Space,Str "as",Space,Str "[bracketed",Space,Str "text]."]]]
+,Para [Str "Here",Space,Str "is",Space,Str "a",Space,Str "footnote",Space,Str "reference,",Note [Para [Str "Here",Space,Str "is",Space,Str "the",Space,Str "footnote.",Space,Str "It",Space,Str "can",Space,Str "go",Space,Str "anywhere",Space,Str "after",Space,Str "the",Space,Str "footnote",SoftBreak,Str "reference.",Space,Str "It",Space,Str "need",Space,Str "not",Space,Str "be",Space,Str "placed",Space,Str "at",Space,Str "the",Space,Str "end",Space,Str "of",Space,Str "the",Space,Str "document."]],Space,Str "and",Space,Str "another.",Note [Para [Str "Here\8217s",Space,Str "the",Space,Str "long",Space,Str "note.",Space,Str "This",Space,Str "one",Space,Str "contains",Space,Str "multiple",SoftBreak,Str "blocks."],Para [Str "Subsequent",Space,Str "blocks",Space,Str "are",Space,Str "indented",Space,Str "to",Space,Str "show",Space,Str "that",Space,Str "they",Space,Str "belong",Space,Str "to",Space,Str "the",SoftBreak,Str "footnote",Space,Str "(as",Space,Str "with",Space,Str "list",Space,Str "items)."],CodeBlock ("",[],[]) "  { <code> }",Para [Str "If",Space,Str "you",Space,Str "want,",Space,Str "you",Space,Str "can",Space,Str "indent",Space,Str "every",Space,Str "line,",Space,Str "but",Space,Str "you",Space,Str "can",Space,Str "also",Space,Str "be",SoftBreak,Str "lazy",Space,Str "and",Space,Str "just",Space,Str "indent",Space,Str "the",Space,Str "first",Space,Str "line",Space,Str "of",Space,Str "each",Space,Str "block."]],SoftBreak,Str "This",Space,Str "should",Space,Emph [Str "not"],Space,Str "be",Space,Str "a",Space,Str "footnote",Space,Str "reference,",Space,Str "because",Space,Str "it",SoftBreak,Str "contains",Space,Str "a",Space,Str "space.[^my",Space,Str "note]",Space,Str "Here",Space,Str "is",Space,Str "an",Space,Str "inline",Space,Str "note.",Note [Para [Str "This",SoftBreak,Str "is",Space,Emph [Str "easier"],Space,Str "to",Space,Str "type.",Space,Str "Inline",Space,Str "notes",Space,Str "may",Space,Str "contain",SoftBreak,Link ("",[],[]) [Str "links"] ("http://google.com",""),Space,Str "and",Space,Code ("",[],[]) "]",Space,Str "verbatim",Space,Str "characters,",SoftBreak,Str "as",Space,Str "well",Space,Str "as",Space,Str "[bracketed",Space,Str "text]."]]]
 ,BlockQuote
  [Para [Str "Notes",Space,Str "can",Space,Str "go",Space,Str "in",Space,Str "quotes.",Note [Para [Str "In",Space,Str "quote."]]]]
 ,OrderedList (1,Decimal,Period)