xsl:try

In conjunction with xsl:catch, the xsl:try instruction allows recovery from dynamic errors occurring within the expression it wraps.

Category: instruction
Content: ( sequence-constructor , xsl:catch , ( xsl:catch | xsl:fallback )* )
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element

Attributes

`select?`	`expression`	The expression to be evaluated by the instruction may be defined either by a `select` attribute, or by an enclosed sequence constructor.
`rollback-output?`	`boolean`	The value `no` is used to relax the requirement to recover result trees when failures occur in the course of evaluating the `xsl:try` instruction. The default is `yes`. (This attribute had no effect prior to Saxon 9.9.)

Saxon availability

Available in XSLT 3.0. From Saxon 9.8, available in all editions. Implemented in Saxon-PE and Saxon-EE since Saxon 9.6. Available for all platforms.

Notes on the Saxon implementation

Saxon 9.9 no longer ignores the value of the rollback-output attribute. If set to "no", when the instruction is evaluated in "push" mode, the output of xsl:try is not buffered, but is written directly to the result destination. If a dynamic error occurs, the relevant xsl:catch is effective only if no output has yet been written to that destination.

Details

It is possible to have more than one xsl:catch within an xsl:try; the first one that matches the error is used.

Within the xsl:catch, a number of variables are available in the namespace http://www.w3.org/2005/xqt-errors:

err:code - the error code as a QName
err:description - the error description (error message)
err:value - the error object (if available)
err:module - the URI of the stylesheet module in which the error occurred
err:line-number - the line-number of the source stylesheet where the error occurred
err:column-number - for Saxon this will generally be unknown (-1)

The error can be re-thrown by using the error() function.

Examples

Example 1

The following example shows how to recover from an error in evaluating an XPath expression (in this case, divide-by-zero):

<xsl:try select="salary div length-of-service"> <xsl:catch errors="err:FAOR0001" select="()"/> </xsl:try>

Example 2

The following example shows how to recover from an error in evaluating a sequence of XSLT instructions (in this case, a validation error):

<xsl:try> <xsl:copy-of select="$result" validation="strict"/> <xsl:catch> <xsl:message>Warning: validation of result document failed: Error code: <xsl:value-of select="$err:code"/> Reason: <xsl:value-of select="$err:description"/> </xsl:message> <xsl:sequence select="$result"/> </xsl:catch> </xsl:try>

Links to W3C specifications

XSLT 3.0 Specification