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#### 4.3.1 Help with HTML Documentation

Help using the HTML documentation is invoked with the built-in Emacs command `browse-url`, which displays the relevant help topic in a browser of your choosing. Beginning with version 6.2, IDL comes with the help browser IDL Assistant, which it uses by default for displaying online help on all supported platforms. This browser offers topical searches, an index, and is also now the default and recommended IDLWAVE help browser. The variable `idlwave-help-use-assistant` controls whether this browser is used. Note that, due to limitations in the Assistant, invoking help within IDLWAVE and `? topic` within IDL will result in two running copies of Assistant.

Aside from the IDL Assistant, there are many possible browsers to choose among, with differing advantages and disadvantages. The variable `idlwave-help-browser-function` controls which browser help is sent to (as long as `idlwave-help-use-assistant` is not set). This function is used to set the variable `browse-url-browser-function` locally for IDLWAVE help only. Customize the latter variable to see what choices of browsers your system offers. Certain browsers like `w3` (bundled with many versions of Emacs) and `w3m` (http://emacs-w3m.namazu.org/) are run within Emacs, and use Emacs buffers to display the HTML help. This can be convenient, especially on small displays, and images can even be displayed in-line on newer Emacs versions. However, better formatting results are often achieved with external browsers, like Mozilla. IDLWAVE assumes any browser function containing "w3" is displayed in a local buffer. If you are using another Emacs-local browser for which this is not true, set the variable `idlwave-help-browser-is-local`.

With IDL 6.2 or later, it is important to ensure that the variable `idlwave-system-directory` is set (see Catalogs). One easy way to ensure this is to run the IDL Shell (`C-c C-s`). It will be queried for this directory, and the results will be cached to file for subsequent use.

See HTML Help Browser Tips, for more information on selecting and configuring a browser for use with IDL's HTML help system.

— User Option: idlwave-html-system-help-location `help/online_help`

> Relative directory of the system-supplied HTML help directory, considered with respect to `idlwave-system-directory`. Relevant for IDL 6.2 and greater. Should not change.

— User Option: idlwave-html-help-location `/usr/local/etc/`

> The directory where the `idl_html_help` HTML directory live. Obsolete and ignored for IDL 6.2 and greater (`idlwave-html-system-help-location` is used instead).

— User Option: idlwave-help-use-assistant `t`

> If set, use the IDL Assistant if possible for online HTML help, otherwise use the browser function specified in `idlwave-help-browser-function`.

— User Option: idlwave-help-browser-function

> The browser function to use to display IDLWAVE HTML help. Should be one of the functions available for setting `browse-url-browser-function`, which see.

— User Option: idlwave-help-browser-is-local

> Is the browser selected in `idlwave-help-browser-function` run in a local Emacs buffer or window? Defaults to `t` if the function contains "-w3".

— User Option: idlwave-help-link-face

> The face for links to IDLWAVE online help.