knitr 1.39

MAJOR CHANGES

• Added an argument rel_path to include_graphics(), which defaults to TRUE, meaning that this function will try to convert absolute paths to relative paths automatically. If the conversion fails, it will issue a warning. If you want to suppress the conversion (and the warning), you may use rel_path = FALSE or set the global option options(knitr.graphics.rel_path = FALSE). In the previous version of knitr, this function would always issue a warning when it detects absolute paths (thanks, @davidski @kendavidn, #2119).

MINOR CHANGES

• For knitr source documents that generate .tex output documents (such as .Rnw and .Rtex), the LaTeX package xcolor will be used instead of color (#2085). This may cause option clashes if xcolor is already loaded by users with options, e.g., \usepackage[dvipsnames]{xcolor}. If this happens, you may set the package option knitr::opts_knit$set(latex.options.xcolor = 'OPTIONS') where OPTIONS is the options you used for xcolor, e.g., dvipsnames.

• The evaluation of chunk options written after #| using the YAML !expr syntax will be delayed until before the chunk is to be evaluated (#2120).

knitr 1.38

NEW FEATURES

• The chunk option file can take a vector of file paths now, i.e., this option can be used to read more than one file (e.g., file = c("foo.R", "bar.R").

• Added a new engine named exec (#2073) to execute an arbitrary command on the code chunk, e.g.,

  ```{exec, command='Rscript'}
  1 + 1
  ```

  The above code chunk executes the Rscript command with the chunk body as its input (which basically means executing the R code in a new R session). See the example #124 in the repo https://github.com/yihui/knitr-examples for more info.

  There exists several command-based engines in knitr, such as awk, bash, perl, go, and dot, etc. This new exec engine provides a general mechanism to execute any command that users provide. For example, the code chunk

  ```{bash}
  echo 'Hello world!'
  ```

  is equivalent to the chunk using the exec engine and the bash command:

  ```{exec, command='bash'}
  echo 'Hello world!'
  ```

  With this new engine, we no longer need to provide or maintain other simple command-based engines. For example, to support TypeScript (#1833), we only need to specify command = 'ts-node' with the exec engine.

  If the command has significant side-effects (e.g., compile source code to an executable and run the executable, or generate plots to be included in the output), it is also possible to create a new engine based on the exec engine. The example #124 in the knitr-examples repo has provided a gcc example.

  We'd like to thank @TianyiShi2001 for the inspiration (#1829 #1823 #1833).

• Added a new engine ditaa based on the exec engine to convert ASCII art diagrams to bitmaps via the ditaa command (thanks, @kondziu, #2092).

• Added two new chunk options, class.chunk and attr.chunk, for R Markdown output. These options can enclose the whole chunk output (source and results) in a fenced Div. Their syntax follows other chunk options with the similar names class.* and attr.* (e.g., class.source and attr.source). For example, class.chunk = "foo" would wrap the chunk output inside ::: {.foo} and ::: (thanks, @atusy, #2099).

• Added a new chunk option lang to set the language name of a code chunk. By default, the language name is the engine name. This is primarily useful for syntax highlighting the source chunks in Markdown-based output. Previously the lang option was only available to a few engines such as verbatim and embed. Now it is available to all engines.

• Added a new wrapper function rnw2pdf(). It allows users to specify an arbitrary output file path, clean the intermediate files, and stop when any error occurs in knitting (thanks, @shrektan, #2113).

• New calling.handlers option for opts_chunk$set() to register calling handlers within chunks. See ?evaluate::new_output_handler for details.

MAJOR CHANGES

• The minimal required version of R was bumped from 3.2.3 to 3.3.0 (thanks, @essemenoff, #2100).

• The working directory under which chunk options are evaluated has been changed to the directory of the source document by default. If the package option root.dir is set to a different directory, that directory will be used as the working directory (#2081).

• include_graphics() will expand ~ in the image paths now and also warn against absolute paths (thanks, @kcarnold, #2063).

• opts_chunk$set() returns values of old chunk options after setting new chunk options now, instead of returning NULL, which can make it a little simpler to reset chunk options, e.g., you can temporarily change a few chunk options and save them with old = opts_chunk$set(error = FALSE, fig.height = 3), and reset them later with opts_chunk$set(old). This works for any other objects in knitr that have the $set() methods, such as opts_knit, opts_hooks, knit_hooks, knit_engines, and so on.

MINOR CHANGES

• The chunk option fig.scap has been added to eval.after in opts_knit (thanks, @knokknok, #2061).

BUG FIXES

• Chunk options defined in the #| style are not recognized when the code chunk is indented or quoted (thanks, @mine-cetinkaya-rundel, #2086).

• Fixed a bug in Sweave2knitr() #2097 (thanks, @chroetz).

knitr 1.37

NEW FEATURES

• Added a new chunk option named file so that the chunk content can be read from an external file. Setting the chunk option file = "test.R" is equivalent to using the chunk option code = xfun::read_utf8("test.R").

• For R Markdown documents, code chunks can be embedded in a parent code chunk with more backticks now. For example, a code chunk with four backticks can contain code chunks with three backticks. One application is to conditionally include some verbatim content that contains code chunks via the asis engine, e.g.,

  ````{asis, echo=format(Sys.Date(), "%w") == 1}
  Some conditional content only included when report is built on a Monday
  
  ```{r}
  1 + 1
  ```
  
  On another day, this content won't be included.
  ````

  Note that the embedded child code chunks (e.g., in the asis chunk above) are not parsed or evaluated by knitr, and only the top-level code chunk is parsed and evaluated.

• Added a new engine named comment to comment out content, e.g.,

  ````{comment}
  Arbitrary content to be commented out.
  
  ```{r}
  1 + 1
  ```
  
  The above code chunk will not be executed.
  Inline code like `r pi * 5^2` will be ignored, too.
  ````

  Note that if any line of the content to be commented out contains N backticks, you will have to use at least N + 1 backticks in the chunk header and footer of the comment chunk.

• Added a new engine named verbatim mainly for R Markdown documents to output verbatim content that contains code chunks and/or inline expressions, e.g.,

  ````{verbatim}
  We can output arbitrary content verbatim.
  
  ```{r}
  1 + 1
  ```
  
  The content can contain inline code like
  `r pi * 5^2`, too.
  ````

  By default, the verbatim content is placed in a fenced default code block:

  ````default
  We can output arbitrary content verbatim.
  
  ```{r}
  1 + 1
  ```
  
  The content can contain inline code like
  `r pi * 5^2`, too.
  ````

  You can change the default language name of the block via the chunk option lang, e.g., lang = 'markdown' will output a code block like this:

  ````markdown
  We can output arbitrary content verbatim.
  
  ```{r}
  1 + 1
  ```
  
  The content can contain inline code like
  `r pi * 5^2`, too.
  ````

  To disable the language name on the block, use an empty string lang = ''.

  The difference between the verbatim and asis engine is that the former will put the content in a fenced code block, and the latter just output the content as-is.

  You can also display a file verbatim by using the chunk option file, e.g.,

  ```{verbatim, file="test.Rmd"}
  ```
  

  This engine also works for other types of documents (e.g., Rnw) but it will not allow for nested code chunks within the verbatim code chunk.

• Added a new engine named embed to embed external plain-text files. It is essentially a simple wrapper based on the verbatim engine, with the chunk content read from an external file and default language guessed from file extension. That is,

  ```{embed, file="foo.R"}
  ```
  

  is equivalent to

  ```{verbatim, file="foo.R", lang="r"}
  ```
  

  If you provide the chunk option file to the embed engine, it will read the file and show its content verbatim in the output document. Alternatively, you can specify the file path in the chunk body, e.g.,

  ```{embed}
  "foo.txt"
  ```
  

  The quotes are optional but can be helpful for editors (e.g., RStudio IDE) to autocomplete the file paths.

  The syntax highlighting language name is from the filename extension by default, and you can override it with the chunk option lang (e.g., file = "foo.sh", lang = "bash") which is then identical to the verbatim engine.

BUG FIXES

• The chunk option child also respects the package option root.dir now (thanks, @salim-b, https://community.rstudio.com/t/117563).

• Fixed a LaTeX error "Package xcolor Error: Undefined color `fgcolor'" with .Rnw documents (thanks, Kurt Hornik).

MINOR CHANGES

• Improved the (warning) message when unbalanced chunk delimiters are detected in R Markdown documents, to make it easier for users to fix the problem. The message now contains the line numbers of the opening fence and closing fence, as well as the opening and closing backticks. For example, the opening fence may be "````{r}" (four backticks) but the closing fence is "```" (three backticks---should also be four to match the opening fence), or the opening fence is indented " ```{r}" but the closing fence is not "```". Note that this warning message may become an error in the future, i.e., unbalanced chunk delimiters will no longer be allowed.

knitr 1.36

MAJOR CHANGES

• In knitr 1.35, if the indentation of the closing backticks does not match the indentation of the chunk header in an Rmd document, the closing backticks would not be treated as closing fence of a code chunk. This behavior has been reverted because we have discovered several cases in which the indentation was accidental. A warning message will be issued instead, and you are still recommended to fix the improper indentation if discovered.

BUG FIXES

• Fixed a regression in knitr 1.31 that caused package vignettes to generate (tangle) invalid R scripts (thanks, @t-kalinowski @halldc, #2052).

knitr 1.35

NEW FEATURES

• Chunk options can also be written inside a code chunk now after the special comment #|, e.g.,

  ```{r}
  #| echo = FALSE, fig.width = 10,
  #| fig.cap = "This is a long caption."
  
  plot(cars)
  ```
  

  The main differences between this new syntax and traditional syntax (i.e., chunk options in the chunk header) are: 1) the chunk options can be freely wrapped, i.e., you can write them on as many lines as you prefer; 2) you can also use the YAML syntax instead of the comma-separated syntax if you like, e.g.,

  ```{r}
  #| echo: false
  #| fig.width: 10
  ```
  

  Chunk options provided inside a code chunk will override options with the same names in the chunk header if chunk options are provided in both places, e.g.,

  ```{r, echo = TRUE}
  #| echo = FALSE, fig.width = 10
  ```
  

  The effective chunk options for the above chunk are echo = FALSE and fig.width = 10.

MAJOR CHANGES

• For R Markdown documents, if the chunk header is indented, the closing backticks (usually ```) of the chunk must be indented with the same amount of spaces (thanks, @atusy, #2047). For example, the following is no longer a valid code chunk because the chunk header is indented but the closing backticks are not:

   ```{r}
  1 + 1
  ```
  

  If you see an error "attempt to use zero-length variable name" when knitting an Rmd document, it may be because of this change, and you may have indented the chunk header by accident. If that is the case, you need to remove the extra white spaces before the chunk header.

  The same problem applies to blockquotes, i.e., > before ```. If you quote the chunk header, you have to quote the footer as well, e.g.,

  > ```{r}
  1 + 1
  ```
  

  The above unbalanced code chunk needs to be corrected to:

  > ```{r}
  > 1 + 1
  > ```
  

  Quoting the chunk body is optional but recommended.

BUG FIXES

• Fixed a regression in v1.34: now blank lines in code chunks are stripped only when collapse = FALSE but no longer stripped by default when collapse = TRUE. If you prefer blank lines to be always stripped, set strip.white = TRUE globally or on the per chunk basis (thanks, @IndrajeetPatil, rstudio/rmarkdown#2220, #2046).

• In knitr::combine_words(), when words is length 2 and and = "", sep will now be used (thanks, @eitsupi, #2044).

• For R Markdown documents, if the chunk output contains N backticks, the output hook will use N + 1 backticks to wrap the output, so that the N verbatim backticks can be correctly preserved (thanks, @atusy, #2047).

knitr 1.34

NEW FEATURES

• Added a package option latex.tilde so that users can customize the tilde symbol, e.g., you can set knitr::opts_knit$set(latex.tilde = "\\hlopt{\\scriptsize{\\ensuremath{\\sim}}}"). This is because the default tilde is too high in the PDF output, and it's often more desirable to use a middle tilde instead (thanks, @brry #1992, @jaredlander #492).

• For the tikz engine, the class options of the standalone document classs can be specified via the chunk option engine.opts$classoption (thanks, @XiangyunHuang, #1985). The default value is tikz, i.e., \documentclass[tikz]{standalone} is used by default.

• Added the ability to pass additional arguments to dvisvgm when using the tikz engine with fig.ext = "svg" by using dvisvgm.opts in engine.opts (thanks, @andrewheiss, #2039). Recent versions of dvisvgm now allow you to embed fonts into SVG files as base64-encoded WOFF files, so tikz chunks can embed fonts using like so: ```{tikz, fig.ext="svg", engine.opts=list(dvisvgm.opts = "--font-format=woff")}.

• Added a new targets engine (ropensci/targets#503, @wlandau). Details: https://books.ropensci.org/targets/markdown.html.

• The chunk option cache.globals can take values TRUE and FALSE now (in addition to a character vector). When FALSE, it tries to find all symbols in the code chunk, no matter if they are local or global variables. When NULL or TRUE, it tries to find all global variables (thanks, @knokknok, #1898).

MAJOR CHANGES

• An error is now thrown when an inline code result is not coercible to character. This has always been the assumed behavior but it happens to be different in certain formats with unknown automatic coercion. This is now enforced to prevent any unexpected output. An inline code expression must evaluate to a character vector or an object coercible by as.character() (#2006).

• The markdown package has been moved from Imports to Suggests in knitr's DESCRIPTION, which means it is no longer a hard dependency but has become a soft dependency of knitr (#1864). One consequence for package developers is that if you use the vignette engines based on markdown (such as knitr::knitr), you will have to explicitly declare the (soft) dependency on markdown, because the implicit dependency through knitr is no longer there.

• For R packages that use the knitr::rmarkdown engine to build their vignettes, rmarkdown must be declared as a dependency in the package DESCRIPTION (e.g., in Suggests). Previously, knitr would fall back to using the markdown package to build vignettes if rmarkdown is not declared (#1864, #2020).

• write_bib() only uses the first URL if multiple are found in a package (#2028).

MINOR CHANGES

• The attribute data-external="1" will be added to <iframe>s generated by include_url() to prevent Pandoc from embedding the URL as base64 data (thanks, @IndrajeetPatil, https://stackoverflow.com/q/67477667/559676).

• The chunk option strip.white = TRUE used to work only when the chunk option collapse = FALSE. Now the two options are independent, i.e., strip.white also works when collapse = TRUE (thanks, @kbvernon, #2011).

• When building R Markdown vignettes but Pandoc is not available, the vignette engine will emit a message instead of a warning before falling back to using the markdown package.

• The internal function is_abs_path() has been removed. Users (if any) should use the exported function xfun::is_abs_path() instead.

BUG FIXES

• Fix an issue with the RStudio IDE when using knitr::include_url() or knitr::include_app() in interactive Notebook mode. This will no more cause an error but print the list object as is (thanks, @systemnova, #2015).

• Fix a regression with fig.keep chunk option used in chunks with only one figure where the figure was not showing in output (thanks, @fmichonneau, #1993).

• Allow vignettes to be tangled (and output compared) in R CMD check if they have a corresponding .Rout.save (thanks, @lentinj, #2018).

knitr 1.33

NEW FEATURES

• Exported the internal functions sew() (previously named wrap()) and is_low_change() to make it possible for other graphics systems such as rgl to work in knitr like base and grid graphics in base R (thanks, @dmurdoch, #1892 #1853).

• For sql code chunks, parameterized queries will be executed through native database api if the chunk option params is provided (thanks, @byapparov, #1987).

BUG FIXES

• Reverted the fix for #1595 since it caused problems in kableExtra (thanks, @bttomio, haozhu233/kableExtra#607), and applied a different fix to the original problem (i.e., add {} before [).

MAJOR CHANGES

• The internal S3 generic function wrap() has been renamed to sew().

MINOR CHANGES

• For package vignettes that use the vignette engine knitr::docco_linear or knitr::docco_classic, knitr will signal an error during R CMD build if the markdown package is not declared as a soft dependency in the Suggests field in DESCRIPTION. The same treatment has been applied in the previous version of knitr for the vignette engine knitr::knitr (#1864).

• R CMD build will signal an error when a package uses R Markdown vignettes to be build with the rmarkdown package but the rmarkdown package is not installed (thanks, @nsheff, #1864).

• The force_v1 argument of knit2html() defaults to getOption('knitr.knit2html.force_v1', FALSE) now, which means its value can be configured via a global option.

knitr 1.32

NEW FEATURES

• The chunk option ref.label can be used to reuse code from other code chunks in the current code chunk. Now it can also accept a character vector of chunk labels wrapped in I() so that the chunk options of other code chunks can also be applied to the current chunk. For example, if we have a chunk ```{r, chunk-a, echo=FALSE, results='asis'}, the chunk ```{r, chunk-b, ref.label=I('chunk-a')} will inherit both the code and chunk options from chunk-a (e.g., echo=FALSE and results='asis'), but chunk-b can still override these chunk options, e.g., the actual chunk options of ```{r, chunk-b, echo=TRUE} will be echo=TRUE and results='asis'. If you want to use one code chunk with several chunk options for multiple times, and each time you want to change a small subset of the chunk options, you may use this approach ref.label = I() to avoid typing most chunk options over and over again (thanks, @atusy, #1960).

• The chunk option opts.label gained a new usage. It used to mean labels in knitr::opts_template (see the help page if you are not familiar with this object). Now it can also be used to specify the labels of other code chunks, from which the chunk options are to be inherited to the current chunk. For example, ```{r, chunk-b, opts.label='chunk-a'} means that chunk-b will inherit chunk options from chunk-a. Local chunk options in a chunk (if exist) will override inherited options. For the new features about both chunk options ref.label and opts.label, see the detailed documentation and examples at https://yihui.org/knitr/options/ (thanks, @atusy, #1960).

• The internal code to process R code chunks was factored out into the language engine R, which can be obtained via knit_engines$get('R') now (thanks, @abhsarma, #1963).

• Added arguments dir and envir to load_cache() to specify the working directory and environment into which the cached objects are loaded. By default, all cached objects are loaded into the global environment, which may not be desirable (thanks, @LTLA, #1905).

• The internal function html_screenshot(), which takes screenshots of HTML widgets and Shiny apps in knitr documents, now prefers the webshot2 package over the webshot package. This is because the backend of the webshot package is PhantomJS, which has been archived since 2018. If webshot is still preferred, use the chunk option opts_chunk$set(webshot = "webshot") (thanks, @atusy #1918, @LouisStAmour #1858).

• Added a new engine, bslib, which is a special scss/sass engine for writing Sass code that wants to leverage Bootstrap Sass. It's primarily designed to work with rmarkdown::html_document_base's theme parameter (when it represents a bslib::bs_theme()), but the engine can be used anywhere a bslib::bs_theme() is set globally with bslib::bs_global_set() (thanks, @cpsievert, #1666).

• When the chunk option include = FALSE, error = TRUE used to be ignored, i.e., errors are signaled nonetheless (causing the knitting process to fail). To avoid this problem, you can now use the numeric value error = 0 so that knitr will not check the include option, i.e., knitting will not fail even if include = FALSE and an error has occurred in a code chunk, which you wouldn't notice (thanks, @rundel, #1914).

• When processing package vignettes that require rmarkdown or markdown, we now check that it is declared as a package dependency in the DESCRIPTION file (thanks, @dmurdoch, #1919).

• For tikz code chunks, a new option engine.opts$extra.preamble allows arbitrary LaTeX code to be inserted into the preamble of the template. This allows loading of additional LaTeX and tikz libraries without having to recreate a template from scratch (thanks, @krivit, #1886).

BUG FIXES

• Fixed an issue where code source and results would not show when using a numeric vector in fig.keep to select all plots (thanks, @dongzhuoer @ajrgodfrey #1579, @cderv #1955).

• Graphical parameter par(col =) is now preserved as expected in following chunks when knitr::opts_knit$set(global.par = TRUE) (thanks, @arnonl, @RolandASc, #1603).

• Fixed an issue with kable(format = "latex", booktabs = TRUE) when the first cell of the table stats with [ (thanks, @jonnypenarth, #1595).

• For child documents, include_graphics(error = FALSE) is the default now (#1957).

• For Rnw documents, the commented %\begin{document} will no longer cause trouble (thanks, @NewbieKnitter @shrektan, #1819).

• Fixed an issue with the chunk option fig.alt causing figures to disappear in rmarkdown::word_document() output. This option is currently supported for HTML output only. If provided for office output in rmarkdown, it will emit a warning and be ignored (#1966).

• Spaces in messages were not properly escaped in .Rnw documents (thanks, @elbersb, #1978).

• The hook hook_pdfcrop() did not crop figures generated by the tikz or dot engine (thanks, @giabaio yihui/xaringan#285, @cderv #1923).

MINOR CHANGES

• For Rnw documents, if a chunk's output ends with \n, knitr will no longer add another \n to it (thanks, @krivit #1958, @jpritikin 1092).

• For kable(x, format = 'simple'), it no longer generates a pipe table but a simple table instead when x has only one column (thanks, @alusiani, #1968). For kable(x, format = 'pipe'), it no longer warns when x has no column names, but just generate an empty table header.

• For tikz code chunks, the default LaTeX template uses \documentclass[tikz]{standalone} instead of \documentclass{article} and \usepackage{preview} now (thanks, @XiangyunHuang, #1985).

knitr 1.31

NEW FEATURES

• Exported the functions pandoc_to() and pandoc_from() to get the output and input Pandoc format respectively when knitting R Markdown documents (thanks, @cderv, #1951).

• Added a new chunk option fig.alt for users to specify the alternative text in the alt attribute of the <img> tag (images). Previously, the alt attribute takes value from the chunk option fig.cap (it still does so if fig.alt is NULL). If there are multiple plots/images in a chunk, you can pass a character vector to fig.alt, and it will be applied to individual images (thanks, @cderv, #1900).

• include_url() and include_app() can now take a vector of URLs (thanks, @cderv, #1948).

• The sql engine now correctly captures error with the chunk option error = TRUE (thanks, @colearendt, rstudio/rmarkdown#1208).

• The chunk option collapse = TRUE now works as expected when the chunk option attr.* or class.* is provided. By this change, The chunk option collapse = TRUE forces attr.* and class.* be NULL except for the chunk options attr.source and class.source (thanks, @aosavi @cderv @atusy, #1902 #1906).

• New links added in ?knitr::kable() help page to the Rmarkdown Cookbook relevant pages.

• The table label can be disabled via kable(label = NA) now (thanks, @NickCH-K, #1937).

• The table.attr argument in kable(.., format = 'html') can take the value from the global option knitr.table.html.attr now (thanks, @cderv, #1922).

• Added a new argument oxford_comma to the function combine_words() (thanks, @thompsonsed, #1946).

• The label prefix of tables generated by kable() can be customized via the package option label.prefix in opts_knit now. This option takes a named character vector, and the default is knitr::opts_knit$set(label.prefix = c(table = 'tab:')). If you want to use a different prefix such as tbl, you may set the option to c(table = 'tbl:') (thanks, @luispfonseca, #1890).

• The global option options(knitr.device.fallback = TRUE) can be used to allow the graphical device specified in the chunk option dev to fall back to other usable devices if the specified device is not operational. Users can provide a list of fallback devices via the global option, e.g., options(knitr.device.choices = list(png = c('jpeg', 'svg'), jpeg = c('tiff'))), which means the png device can fall back to jpeg and svg (the first operational device in the list is used) and jpeg can fall back to tiff.

BUG FIXES

• Line numbers in error messages are incorrect when the error occurs in a child Rmd document (thanks, @cderv @khughitt, #1945).

MAJOR CHANGES

• Previously knit_exit() in a child document would not terminate the knitting process of its parent document. Now it will terminate the whole process by default. You can use knit_exit(fully = FALSE) to exit the child document only (thanks, @davidchall, #1810).

MINOR CHANGES

• Vignette engines for R Markdown vignettes no longer check for availability of pandoc-citeproc since it has gone since Pandoc 2.11.

knitr 1.30

NEW FEATURES

• Added knitr::hooks_*() functions to get a list of output hooks for a specific format. Previously, these hooks only exist inside the knitr::render_*() functions, and users do not have direct access to them. Now they can be accessed directly, e.g., via knitr::hooks_markdown() to get a list of output hooks for R Markdown documents. You can also set the output hooks individually, e.g., knitr::knit_hooks$set(knitr::hooks_markdown()['source']) only sets the source ouput hook. See more on output hooks at https://yihui.org/knitr/hooks/#output-hooks and https://bookdown.org/yihui/rmarkdown-cookbook/output-hooks.html (thanks, @cderv, #1889).

• Added an argument lib.loc to knitr::write_bib().

BUG FIXES

• The option fig_caption = FALSE for rmarkdown::html_document() was unable to suppress the figure captions in some cases.

• The internal function fix_options() should be called after option hooks are executed (thanks, @atusy, #1876 and #1877).

• When the option options(OutDec = ) is set to a value other than ".", percentages in the chunk options out.width and out.height do not work (thanks, @omgitsmoe, #1887).

MINOR CHANGES

• knitr::write_bib() removes pairs of single quotes in the titles of citation entries now.

• knitr::write_bib() uses the URL in the package DESCRIPTION if it is provided, instead of the canonical CRAN URL for the package.

• hook_pdfcrop() and plot_crop() will work only when both programs pdfcrop and ghostscript have been installed. Previously only pdfcrop was checked (thanks, @dalupus, #954).